With some possible exceptions, why do most talk show hosts always seem to be seated on the right with the guest on the left? Is there a particular reason for this or is it just how it is?
Because it makes them seem powerful. In Western culture, we read from left to right, and we watch theater and television that way, too. Our eyes end up on the right side of the screen—where the host sits (also known as stage left). In the theory of stagecraft, it's understood that a rightward placement telegraphs royalty. So no matter how famous the guest may be, sitting to the left makes him or her seem subservient. Late-night hosts also sit slightly upstage (farther back and slightly elevated) from their guests, which likewise reinforces the notion of a power imbalance.
Stage designers hold that guests make a stronger impression if they enter from stage left, crossing in front of the host and shifting the audience's focus ever so briefly. Perhaps that's why David Letterman—famous for the occasional cutting takedown—makes his guests march in from the weaker stage right. Colbert [when he was host of Comedy Central's The Colbert Report] plays with this dynamic most self-consciously. Guests wait in the interview area while Colbert makes his entrance. He keeps the focus on himself at all times.
However, these days there are exceptions:
British comedian James Corden made his debut as host of CBS' Late Late Show on Monday, promising at least one big change to the familiar U.S. late-night talk show format before he even started.
"We’re gonna bring all our guests out at the same time, so all of our guests will sit together for all of the chat segments of the show," Corden told KPCC last week.
During interviews, Corden sits in an office chair to the left of his guests [...], who all share a couch. This literally puts him on the same level as the celebrities, theoretically allowing for more casual, more intimate conversation.
Interviewing without a desk, as well as inviting multiple celebrities on stage at once, is an intentional homage to iconic U.K. chat show host Graham Norton. On The Graham Norton Show, there is no desk. Norton sits to the left of his guests, who share a single long couch.
Bravo's raucous Watch What Happens: Live has perhaps the most unique set of any American late-night show. Not only does host Andy Cohen lack a desk, but he sits to the left of his guests. (And this is to say nothing of the on-stage bar.)
I presume you're talking about the US.
In the UK they tend to be camera left, though not always.
So, I'd say it's a false premise, but it might be for similar reasons to why you guys drive on the other side... because someone did it first and it was simpler to go the same way than fight it.
Comments/research would indicate this was Johnny Carson - that others tried different approaches but they weren't as well-received in the early days.
He pioneered the powerful 'boss behind the desk' style, which others have since copied.
Whether this was a previously-studied psychological influence, putting the host in the most favourable position, or not, seems moot. Such inference is easy to make after the fact, but it may have simply been some set designer's idea of how to make the studio look "interesting". We may never know.
I have, incidentally, only realised whilst doing this research that what I have always thought of as "Letterman-style" is actually "Carson-style"... but I'm a Brit and have never seen Carson.
Presumably, as no-one in the UK would ever have seen Johnny Carson at the time - international broadcasts being extremely rare in those days - this couldn't influence their perceptions, and a much less power-hungry chat show style developed, by independent thought process.
The idea of 'host as demigod' presiding over people who were, in reality far bigger figures in the public perception seems somewhat alien to the British culture. (Conversely, you could say we were more fawning, but I guess that is all dependant on which side of the pond you originated;)
I googled some mainstream UK examples of the 'more equal-power' appearance of UK chat shows across the years, with the host on no particular side, but the staging and seating far more egalitarian, with host and guest in identical chairs as the norm [though there are exceptions] ...
Wogan - left and right
Ross - left and right
who seems to have actually occasionally embraced the Carson/Letterman-style, though swapped sides
Parkinson - left
Norton - left ... + famous sofa
Last Leg - right [though technically this is a 3-man presenter team, one on the desk and 2 on the sofa, with guests joining on the sofa at camera right of the 2 presenters.]
Frost - left
It's not definitive, but it shows even over here it's not set in stone.
After comments, some more political-style shows...
Paxman - left and right
Marr - left and right
Reading some of the other answers, it would seem, perhaps, that the UK has eschewed the US-style "behind the desk, position of power" almost entirely and gone for a more "equal-power" approach; the only similarity being Jonathan Ross, in what is a fairly obvious mock-up of the Carson/Letterman-style, though interestingly swapped right for left.
Slate has an article from 2010 discussing this. Their initial argument is that the right side of the screen is perceived to be more powerful by audiences in the western world. Later in the article they say that when Steve Allen initially hosted the Tonight Show, the dynamics of the stage that was used favored a screen right desk. After that, people generally didn't want to mess with success, and that subsequent shows that tried alternate approaches were not so successful (although even they give some examples which were at least somewhat successful).
Color me unconvinced by the powerful position argument, although admittedly I'm no expert in this field. Personally, I'm more convinced by the idea that the precedent of having the desk on the right side of the screen was established in the early days of talk shows, it has come to be the expected standard (in the U.S. anyway), and most folks won't want to do otherwise now unless they have a reason to do so. This is backed up (in my mind, at least) by something I read a while back about Johnny Carson - that article stated that everyone wanted to copy him, once he experienced the success he had on the Tonight Show. Unfortunately, I couldn't dig up that article.
Because nothing succeeds like success.
The two longest-running chat shows are The Tonight Show in the US, and The Late Late Show in Ireland.
The Tonight Show had Johnny Carson, and then later hosts, sitting to the right behind a desk and guests to the left.
The Late Late Show had Gay Byrne sitting to the left, with guests either on a sofa or a bank of chairs to the right, as they went through a few different set designs in this regard.
It wouldn't be surprising if either contemporary competitors or people who had grown up watching television were more likely to favour the right if they were American and more likely to favour the left if they were Irish, since America and Ireland both had long-standing successful models to emulate.
But the very fact that the two oldest such shows take the opposite approach shows that neither is the approach always taken. And in places without such long-standing models that are (or were) at the high point of the Zipf distribution that ratings tend to have, it's not surprising to find that the neither side predominates.
It's also worth observing that while game shows often have a format in which it makes sense to have the host to one side and the contestants to another, there's even more variety. In terms of staging the pressures on the choice of side are pretty much the same as with chat shows, so if one was objectively the one to go for (or even consistently subjectively the one to go for) we'd see one side predominate. But game shows don't have the same impulse to try to copy Johnny Carson.