While you may get lucky at a school or two, I really doubt that many admissions officers are going to sit down and right you a summary of why you didn't get accepted. Not only is it not really feasible given their schedule, but your rejection is usually a combination of many things (when compared to the large applicant pool)...so, if you even did get a response, it would go something like "while you are a strong applicant, there is not room to fit everyone, bla bla bla." These types of questions from applicants are usually filtered out by the administrative staff and usually don't even get to the person addressed, because of the sheer number of requests they get a day. I know this is no excuse for the mistake, just realize it may not be the dean's fault that you got the wrong standardized letter. If it makes you feel any better, many acceptance letters don't even include any personal information (at least that I am aware of). In fact, Pitt was the only one that included some of my own activities in the bulk of the acceptance letter. Anyway, like I said before, sorry for the bad news and the mistake. Good luck with the other schools.
...if you really want to know why you didn't get accepted though, I really think calling would be the most efficient way, although I am not guaranteeing anything.
I'm curious too because I thought all post interview decision letters were sent out in March. Sorry to hear about the bad news.
