I just realized that Rivera is the flip side of Rick Porcello, in that his fWAR is about 50% lower than his bWAR.
Rivera's fWAR is more than double Nen's, so the volume is a big factor.
I do tend to agree that being on those Yankee teams made Rivera seem even better than he was.
As for the unanimous vote thing, I've always thought the attention paid to that, in general, is stupid.