Katamari Damacy...while it's true that innovative games released on both GameCube and PS2 usually sell better on GameCube, I'm sure there are successful, innovative games on the PS2. The problem is the system is so flooded with games that fewer of these "sleeper" games stand a chance of becoming hits. Once one does, though...chances are it will not sell better on Cube. I don't know what Katamari's sales were on PS2, but I doubt that it would have sold more than 250,000 copies on the GameCube, and that's assuming it would get a lot of coverage from the media, especially Nintendo Power.
Seaman...I've always been interested in this game, it's one more point for PS2 if I ever go out to buy another console. I agree PS3 would be smarter, maybe Sega thinks PS3 will be too expensive!