Doing a port between the PS3 and 360 is a piece of cake, if your engine is well written and designed for this purpose -- which, by the way, describes most major 3rd party engines.
It doesn't cost much more to do PS360 cross-plat games, than exclusives, past the engine's first iteration.
As long as the 360+PS3 hold onto their
((average per-game attach) * (combined console count)) / dev costs
being greater than the Wii's
(per-game attach * consolecount) / dev costs
...there will be PS360 crossplat games, and the Wii's 3rd party support will suffer for it. Given the crappy attach rate and lack of a distinct demographic target for the Wii, the PS360 will be just fine for a long while. The PS3 and 360 have a substantial cross-console similarity that no previous console generation has really had -- which will extend the lifespans of both consoles against the dominating Wii for a long time to come.
If the 360 was not doing so well this holiday, then PS3 fans (and 360 fans) would be much more upset, I think.
