Valve, makers of Halflife et al, has published some survey results on what people actually have in their machines. Note that this is a survey of gamers (or they wouldn't be using Steam) and I find it quite interesting:
http://www.steampowered.com/status/survey.html
It seems that people's machines aren't all that souped up after all, particularly in the graphics department. A third use a board slower than or equal to the reviled 5200 Ultra (which is why I posted it here, of course) and another 10% use a board from the Geforce4 Ti series. If it is the 4200 (which is the most common of those boards) it's not far behind the 5200U. That's not far from half on boards of similar performance to the 5200U. This is more than I expected - had I been a PC gamer, I'd consider anything less than a Radeon 9600 a joke.
So what is the point I'm trying to make? The point is that game developers cannot ignore all these people just yet. While I grant you that the people on Geforce2 MXs should consider an upgrade (unless it's nForce IGP motherboards, where that chip is built in, but then what are they doing gaming?), and some of the ones on Geforce4 Tis may be waiting for the 6600/X600s to grab their next board, many have quite new boards. You can't draw the line at a Radeon 9600 for a couple of years yet. No matter if the game is trying to be another Doom 3 or Far Cry, it has to have options to make the game playable on lesser machines.