[Zigûr]

I suppose it really depends on what dramatic purpose having Elves at the battles in the South serves from the point of view of the films. We can't assume that any motivation or "historical" fact from the books holds true in the "world" of the films; we can only work with what the films give us. I think the point was to show that the people of Middle-earth were not as estranged and disunited as it seemed; if that's the case then the question is whether the second or third film of the trilogy was the better place to demonstrate that.

Frankly I think some Dwarves ought to have shown up too. After all, all bets were off by that point.