[quote name='Josef']I know that some PS2 Greatest Hits games and XBox Platinum Hits games contained some changes in content to the regular versions, but I'm not sure if any of the GameCube Player's Choice titles also had extra/different content.[/QUOTE]
Yeah - some of the fighting games added content, for instance, and while I can't remember which franchise it was (Virtua Fighter or Tekken, I think), there's at least one game that was released only as a Greatest Hits title.
For the GameCube, though, I can't think of any games that had significant changes made.