I think all games should be produced for only 1 or, MAYBE, 2 systems, as multiplatform developement slows down the games production, and keeps all the titles on all the systems from reaching their true potential, as different consoles have different strengths and weaknesses, and its hard to considers these when you've got to juggle the code for three completely different systems.
Although developing a game for a console and the PC is a different matter, as sometimes that can make both games stronger, such as the case of Elder Scrolls III: Morrowind which (despite being delayed umpteen million times
) developed better ways to manage their memory for the PC version when they had to streamline their memory usage so the game would work on XBOX. But I'm not sure if the XBOX version benefited from that as much.
Also another thing that bugs me is when games for different consoles come out at different times. It just sucks...I can't really use big words and laser-targetted wit to explain it, but because of that, some people (like me) feel forced to get a game for a system they didn't want just because the release date is a month or two earlier.