I agree with the competition part, but I don't think that is going to happen so much as we will just have yet another gaming rig. Game devs are going to have 4 platforms to develop for instead of 3. Me, I'm not giving up my computer, and really am mystified at this point why other people just don't go ahead and migrate over. Like, everyone already has a computer, so just save that $500 you'll spend on a new console, spend it on games, spend on a better graphics card, whatever. The only thing Xbox and Playstation have going for them is their respective communities - and really, they just create divisions in the overall community in the end. Xbox players can't play with Playstation players can't play with PC/Mac players.
A decade ago their was a good place for a console. They were less than $200, and you couldn't buy a computer anywhere near that and play top games on it. It's different today, their isn't enough of a price break, and it just makes games more expensive because devs have to deal with all those systems.
And Valve is adding another.