Not getting anything at this point doesn't necessarily mean you're out. I talked with the graduate chair at my school about this a few days ago. He said (at least here) the first round is obvious admits that are going to get in lots of places, and they only expect maybe one out of ten to actually enroll. I'd imagine responding earlier to these types of top applicants makes them more likely to enroll. Once they start to get idea of how many of those people are going to enroll, then they work their way down the list. He also mentioned that occasionally smaller private schools can be more sporadic in their acceptances, because instead of having a graduate chair/committee focusing on admissions, they'll just give your application to professors in your preferred research area. Chicago might be out of the picture (I think they generally get most of their admissions done in one wave), but I'd still hold out hope for Berkeley and Cornell.