Oh, I understand you can replace most software with open source equivalents. Many people, however, probably don't even have a clue what open source is.
And the thing about the games moving, the problem is, it's a bit self defeating. People will not move without the games, and the games will not move without the people.
The final problem is driver support. There are some things that just don't work right under Linux. Winmodems, for example. They're technologically inferior, but they're found in virtually every computer built by an OEM, and many don't run under Linux.