4:3 aspect ratio is in the market since the early days of television. 16:9 came into picture more recently. It is true that 16:9 is becoming more and more popular now a days. But we have not reached the time to forget about them.
Standard 4:3 format aspect ratio
A standard aspect ratio television screen is a TV with a resolution that matches the NTSC or PAL broadcasting standards. These TVs are designed for analog signals and use a square-like 4:3 aspect ratio. Devices with a standard 4:3 aspect ratio are incapable of outputting High Definition content. In this respect, standard format televisions are inferior to widescreen televisions, and there are many other benefits to using widescreen devices which are covered in more detail below.
Standard 4:3 television screens are gradually being phased out, as are standard definition analog television broadcasts. Within consumer electronics shops non-widescreen televisions are becoming increasingly rare. Furthermore, the majority of countries in North America and Europe now have set dates in the near future when these analog signals will be turned off permanently.
Widescreen 16:9 format aspect ratio
The widescreen 16:9 aspect ratio is the image standard of the future, designed to succeed the traditional 4:3 square aspect ratio. To take advantage of the benefits “true” widescreen can offer, you need to own both a widescreen television and videos coded in a 16:9 aspect ratio, such as High Definition television content, which only comes in widescreen format.
Although widescreen 16:9 format is synonymous with High Definition content, 16:9 is also commonly used with standard definition television and DVDs. The reason for this is because DVD film producers and TV broadcasters offer both 16:9 and 4:3 outputs.
Reasons for still using 4:3 aspect ratio:
While the 4:3 aspect ratio is viewed as somewhat dated, it is still very common and is still the standard aspect ratio for computer screens. While it is true that High Definition content is becoming more and more prevalent, the majority of broadcasters still output in a 4:3 aspect ratio. While the same cannot be said for films, if you still watch a lot of VHS tapes of older films then a 4:3 television will allow for the image to take up the screen. Displayed on a 16:9 television it would appear stretched, or would have black borders running along the edges.
Reasons for still using 4:3 aspect ratio:
The benefits of the widescreen aspect ratio format are numerous, so it is easy to see why widescreen devices have become so popular so quickly. These benefits are summarized below.
The future format
In only a few years time, videos in widescreen format will be the only type available. Furthermore, widescreen televisions will soon become the only type of TV available for purchase.
Same size picture as films
All movies are now shot using a 16:9 aspect ratio, meaning if you have a widescreen display device the video will be displayed without the black borders present in 4:3 television screens.
Blu-ray is the next generation DVD format that outputs films in High Definition. To make use of this it is necessary to have a widescreen 16:9 High Definition television.
High definition content
High Definition content is only output in 16:9 aspect ratio resolutions of 1280×720 or 1920x1080.
Increased viewing area
Pictures displayed using a widescreen aspect ratio show 25% more of an image than 4:3 aspect ratio pictures.
So from the above discussion it is quite obvious that 4:3 is phasing out slowly. But still we cannot ignore it totally. Different users still prefer 4:3 to 16:9 for different reasons like cited before. In this forum, you can see some examples. When we would be able to make 16:9 more advantageous and when economy would allow us to make it cheap so that maximum of common people can afford buying HDTV, I think then only producers and broadcasters would stop making in 4:3 ratio.
FYI, Still in third world countries and developing countries like India (Where I belong to by birth) the price is too high for maximum of average people. It starts from around 60K and ends at 300K INR.