Originally Posted by GuitarBizarre

Because if nominations are also votes, then theres a huge bias to recently active posters. If the nominations are nominations, and the votes are seperate, then a person who was only active 10 months ago might get 1 nomination, but that nomination might get more than one vote as people see the name and are reminded of that person.

Theres also the fact it forces people to reconsider their vote at least once, which means more thought goes into it.

On top of THAT, its easier to pick from a small pool of nominees than it is to pick from the whole userbase over a year. You end up with people who didn't nominate anyone, but who will still vote once they see a category contains someone they like.