Don't forget that the main reason for the consoles is, is that most people don't want to have the 'trouble' of games on their computer. Most people want a console, not because of its strength but because they know that when they buy a game, it will work on the console. They just don't want to have wonder if their computer can run it and if they need to have a better computer.
I am speaking as an owner of a high end computer, xbox 360 and a Playstation 3. I prefer gaming on pc because I like modding, tweaking, having more control over my game settings and the ability to play with higher framerates and quality settings. However a console gives me the feeling of really chilling out. When you get home from work or school, just drop on your couch and turn on the tv and console. Especially because I work al day long with a computer, it is sometimes nice to just not have to use the computer but a console which handles everything for you. Ofcourse you could connect your pc to the tv and use a gamepad, but it is not the same.
The light side to exclusives is that the big companies put in a lot of money to make good games and battle each others creativity. Innovative ideas are born at a much more quicker rate because of this. (although there is a lot cheap junk between it 2. B) )
There is also one other thing that the consoles are going to have an advantage from: Natal and Move. The computer doesn't have this. The mayority of the people will just buy this because it is new, it's fresh, it is a gadget. Even if it is not working as they proabably want it to work.