They are standing next to Kraken's carcass and facing the growing threat from East India Trading Company. There is also the first part of that conversation:
Barbossa: Still thinking of running, Jack? Think you can outrun the World?
You know, the problem with being the last of anything...
...by and by, there be none left at all.
Jack: Summoning the Brethren Court, then, is it?
Barbossa: It's our only hope, lad.
Jack: That's a sad commentary in and of itself.
So, Barbossa's remar (that follows the cited part) can be interpreted as "there will be no place left for you to run to".
Jack's response could mean both a disagreement ("the World is the same") or an agreement ("less stuff [to use to hide] in it"). I think that it's deliberately vague, because Barbossa has a facial expression that - to me - shows he's uncertain of the meaning (and he needs Jack to agree).