my guess is, at this point, they simply don't have to.
In the old days Sony could get console exclusives due to massive marketshare and companies (particularly Japanese) familiarity with SCE. Now, with the price of AAA productions getting higher and higher, most companies need to get those games on as many viable consoles as possible to cover high production costs and ultimately make a profit.
Paying for (or 'moneyhatting', as some like to say) a third-party game to remain only on a single console is much more expensive now, as a company will likely consider the revenue they would be losing by not being multi-platform. Companies like MS/Sony/Nintendo have two options right now: co-publish the game with the third-party, thus footing a good deal of the production bill or, in the words of the great Randy Moss- "straight cash, homey" to secure the exclusive.
Sony has concentrated on their first-party exclusives for a while now, as they should IMO. They've also seen MS spend a ton of money on exclusives (and exclusive content, like that massive deal with Rockstar over GTAIV) without significant effect.
If PS4 dominates the X1 the way the PS1 dominated the Saturn or the PS2 dominated the Dreamcast or XBox, PS4 will likely get default exclusives anyway- and without paying out the ass for them too, in theory.
If this console war is close, you might see Sony start digging in their pockets a bit to shore up a few big games. MS will continue trying to get exclusives, too, in order to stay competitive. Either way, there will be some big third-party exclusives this gen I predict.
