Possibly, there are still a lot of people who play games at 800x600 and lower resolutions for screens since a lot of people own lowend and onboard video cards which can't play many games at higher screen resolutions like 1024x768.
But, I got a feeling there is also a large percentage of people who don't know how to change their screen resolution and game quality settings to a lower setting for faster gameplay.
Playing games at 800 x 600 at lower quality is better then choppy, and laggy video gameplay.
According to YouTube based on 800x600 gameplay search I can find videos which shows people playing at 800x600 with okay framerate.
Some people also still have older monitors which only support lower resolutions. I think many people keep reusing their old monitors until they break, or the cost of a higher resolution monitor is cheaper that they can afford one for their video card which supports lower resolutions.
There are also people with poor vision who can't tell the difference between high and low resolution because when they don't wear glasses their vision is less clear, so they might want to adjust the resolution lower for bigger pictures, and faster performance rather then higher resolution which make the screen image not as easy for reading text, and can slow down framerates which is more noticeable with people with good and poor eyesight.
Turning off anti-aliasing and other settings on your Nvidia and ATI videocard software drivers can also make framerates faster because the video card does not have to work as hard displaying A-A and other settings and effects.
