well if they are using the triforce board, wouldnt that make it a Nintendo exclusive? Since it is their board? Or is it that since its Sega, Namco, Nintendo. They can use the board, and put it on any system they want???
Basically the underlying programming is pretty much the same with the GameCube and the TriForce so it's easiest to publish Virtua Striker 4 on GameCube.
For other examples, think Chihiro/Xbox -> OutRun 2 and Naomi/Dreamcast -> loads of Sega arcade ports.
Planet Harrier is likely never to happen. I remember reading a Nagoshi interview in which he was asked about a possible port. His answer was essentially that complaints about the game's difficulty was forcing them to carefully consider it's release. Considering how far we are now into this generation and the control Sammy, I doubt that Harrier ever makes it home. If it does, the PS2 might be the target platform before anyting else.