The transition away from physical media also had a lot to do with it as well - I own licenses to D2 and the expansion, and Starcraft, so I was able to put my keys in, and now if I get a wild hair to play either, I can download them and do that - on either platform, too, which is a bonus. It's a huge benefit for us, and a big cost saving for them, as they don't have to keep making CDs and DVDS for the installers. The Steam model for games sales is the way forward, and Blizzard adopted it.