I was told that basically they just sort of let the strongest applications float to the top and don't keep period "quotas." Certainly it's something they might think about, but periodization matters less than matching up with a professor or two who have similar/related interests. I'm pretty sure I got in because there are two professors with very specific subject fields related to my stated interests. But then again, I haven't talked to most of the professors on this year's adcom recently. (I'm a current student here to stalk the new admits and tell them to come to Open House, so I have heard this from "the source", so to speak, and I could not help but look at the person worrying about two Af-Am lit admits and say, "We must have admitted about 8 of those last year, and hired another person in the field since then! Stop worrying!")
[Edit: I suppose my real point is, don't give up because of what you've heard, until it's over!]