The initial announcement of Counter-Strike: Global Offensive gave us the hope that we could all get along; that you there with your hand-build Intel i7 rig could be playing with a friend who might be sat on his sofa, starting at his giant television, holding a joypad. I wanted that, you (maybe?) wanted that, Valve initially wanted that. Now Valve do not want that. Speaking to Joystiq, Chet Faliszek told them it was because they need to frequently update the PC and Mac versions more frequently.
The beta has proved we want to update not just the beta, but the game itself post-launch frequently on the PC. To do that we need to separate the platforms so one doesn’t hamstring the other. So for that, we have removed the idea of cross-platform play — essentially make all platforms stronger by not mixing them.