I guess the idea is, when you have a new game, you need as many people to know about it as possible. The average person isn't going to know or care about this right now, but we'll talk about it. So, they announce for PC, and people that wouldn't have otherwise talked about it do. The word spreads slowly, meandering around, maybe someone tells somebody not on the internet. Chatty chatty. Then, they cancel the PC version because it's not the best option for their agenda of creating dominance in the console arena. At this point, the hope is that people have been following the game long enough have it stuck in their heads so they grit their teeth and get the 360 version, or the word has spread enough to their friends that they decide to buy it.