The minimum system specs you should target for reaching a wide audience is a sliding window. 4-5 years old machines usually (the vast majority of machines aren't used for more than 6 years). What Cas said is also true. It's getting easier. Just look at something like Space Invaders. It's so cheap (by nowadays standards) that it's done as a tutorial. However, we always tend to exchange that advantage for a more complex design. Well, I think it's great. You can switch to/use a higher level and you can do about any game you like (except those with too much content) as long as you don't use something extremely slow like flash. Oh and basic 3d acceleration becomes also ubiquitous.