My laptop has a DVD player (read only), but my parent's computer does not. Putting games on DVDs definitely saves space; I have noticed this the most on the Playstation 2. Final Fantasy IX took up four CD roms on the Playstation; Final Fantasy X, for the Playstation 2, was just as long, but only took up one DVD-rom. And when I bought Escape from Monkey Island for the Playstation 2 (I have a crappy video card
), it only used one DVD-rom (and, it should be noted, looked better!); the PC version used two cd-roms.
Maybe the game companies assume that most gamers don't have DVD players on their compy. They want as many people to buy their game as possible, so they put them on CDs so more gamers will buy them.
BTW-it is possible to have muti-disc games on DVD-rom...I have two for PS2 (Shadow Hearts Covenant, and Xenosaga Episode II).