Given how poorly games that are delayed by 12 months sell, there must not be much difference between a timed exclusive and an exclusive deal. I am really curious as to the dollar amounts being offered for such deals.
If I was an XBox owner, I would feel cheated if a game I thought was exclusive ended up not being exclusive, and it ended up being more polished on a rival console. As a consumer I would prefer to know if it was a timed exclusive or not, but this would definitely minimize the impact of the exclusivity deal. The only exception to this that I can think of would be GTA on PS2/XBox, where I think everyone knew that it would come to the XBox, but most people got it for the PS2 anwyay.
I think it is a dirty business tactic, but all evidence points to it being a very successful one. Like most people pointed out, it is a lot less risky to invest in a timed exclusive deal on a known franchise than it is to invest in a new IP. And if they don't get a timed exclusive on a game, the tactic shifts to get DLC exclusives. If I didn't already own a console, deals like this could definitely sway me to buy an XBox instead of a PS3.
The only good thing is, seeing that I already made my choice long ago to get a PS3, and since I have no intentions of getting an XBox, I can still play some of these games when they do eventually get ported.