Here, in my opinion, is what the other possible nominees have against them:
MACBETH: A great, probably-Tony-winning performance by Patrick Stewart (and maybe Kate Fleetwood), but not the best production. It may not get a lot of votes from the Shakespeare-loving voters who feel the production doesn't quite respect the text.
THE HOMECOMING: Closed in April. Got very good reviews, but not the best (there were complaints that the production didn't have an edge).
TOP GIRLS: It's non-linear. Not getting the greatest board reviews (of course, there have been plenty of shows this season that didn't get the reviews they got on the boards).
Other revivals, unless I'm missing something, aren't in the running (unless CYMBELINE pulls the surprise nominee and even-bigger-surprise win [which won't happen, but...]).
"Y'know, I think Bertolt Brecht was rolling in his grave."
-Nellie McKay on the 2006 Broadway production of The Threepenny Opera, in which she played Polly Peachum