Seriously, what is MS thinking? I know that fanboys oversell the exclusives angle but at some point they will make a difference.
Although multiplatform games continue to be better on the 360 90% of the time, there are probably less than 1% of gamers who know about that. Now that the PS3 is no longer price constrained, it will simply look like the better deal to most people. Even if potential customers didn't care for the PS3's blu-ray advantage, they would still see it as the system with more games to play.
Most people who want to play Gears or Halo probably got a 360 already. What's out there to entice new buyers?
It has been 4 years since 360 was released, 3 years since PS3. The software that is going to sell these systems is already out. From this point forward, the things that will drive further adoption are the following:
1) Holidays (and, on a more personal and spread-out level, birthdays)
2) More attactive pricing.
3) Further abandonment of the PS2 by software developers.
4) The Unknown. A game changer, something revolutionary that isn't just another piece of hyped up software. Natal? A game that comes out of nowhere?
You're not going to see a in-generation sequel cause a considerable and prolonged spike in sales. It just isn't going to happen.