You're comparing apples to oranges.  Playing catch-up in a market and trying to sustain a sufficient critical-mass in a market are very different things.

Sony needed to improve sales within the first year in a market with two strong competitors to become relevant with software publishers (publishers will give a major competitor like Sony grace at the beginning, but there has to be ROI eventually).  Sony accomplished this.

On the other hand, MS needs to reach a critical mass of systems in the market before the end of the year to remain relevant.  As long as the 360 doesn't fall too far behind the PS3 in total systems sold (they're not competing head on with the Wii because they're attracting very hard-core FPS/RPG gamers), then the publishers will continue to see a reasonable ROI and the software will continue to being released on the 360.

This isn't rocket science.  Unless something really dramatic happens this year or next I don't see any of the consoles "dying out" this generation.  The PS3 was most in danger early to mid last year, but it is now a strong contender.

 This is a very important point and huge advantage for the PS3 over the 360. In the States, the 360 is selling well enough that it's ridiculuous to call it sinking. PS3 is definitely surging and 360 is losing market share, but it's still selling units at a respectable pace. 

Agreed, obviously the biggest part of R&D was accounted for in periods before launch, while after there will be other R&D expenses, far smaller than the initial ones, for the evolution of the project (like the die shrinks, that would have happened anyway for economy and yield reasons even without the additional incentive of resolving the RRoD issue).

My point, though, was that even if those expenses are already accounted for, XBox 360 will have to repay and surpass them with its earnings to say that it's been a successful product and considering game royalties it should need roughly 30 to 40 million consoles  sold to reach this goal. It shouldn't be difficult, even if it should end third this goal is perfectly within its reach, as SW sales are very good and so are royalties, therefore.