The master himself explains why Zelda changed to the new look ...
Go read IGN's story. But to whet your appetite, this pretty well sums it up ...
"One thing I'm afraid of is that people who already saw Link in the very beautiful graphics may be looking forward to the much more sophisticated looking version of him [Space World 2000 footage] in the next Zelda. I do not want to betray them or shatter their expectations, so what we are doing now is making Zelda as unique as possible because uniqueness is something gamers are always looking for. So I can say that we are ready to make that Zelda."
