With game development costs growing to monstrous proportions and trampling the unconventional concepts roaming the streets of less ambitious publishers, it doesn't take a brilliant businessman to realize that multiplatform releases are likely to generate more money than exclusives. It might, however, take a brilliant programmer to carry out that strategy. Since the Xbox 360 and PS3 both embrace the paradigm of parallelism (or really pretty graphics, if you prefer), it has become almost a foregone conclusion that a large number of titles will inevitably wind up on both platforms.
It's not an outlandish conclusion to reach, but the journey may not be as easy as all that. In a recent (and very interesting) Ars Technica interview, Xbox 360 developer Matt Lee points out that porting games between the two systems might be a tad tricky.