There are very few that have that option, but many of them have other obsticles that intefere with upgrading. Sometimes only changing it with the same card only. Some difficulties are different slots, won't fit the chassis and sometimes neighboring components may be in the way. Its just that mobile graphic cards haven't become as universal or as available as desktop cards have become. If you do see a system with changeable gpu's, i'm sure they'll most likely be on the chunky side. I believe there are a couple Dells, Sagers, and Polywell that may have this option at the moment. Still, you'll be limited to what you can replace it with.