Metroid Prime 3 to have much upgraded graphics for 2007 release
"The build of Metroid Prime 3: Corruption seen at E3 is being completely spruced up for its 2007 release and will look MUCH more impressive, rather than merely a shinier edition of MP2 from the GameCube."
So I guess the delay of Metroid Prime 3 had much more to it than just letting the Third Parties have some of the cake for this holiday. I think Retro may have been getting tired of people saying it looks no better than Gamecube(it did, but they didn't really give credit). We'll see how it pans out.