Lo and behold, my question was answered (toward the bottom). I think it was a fair answer, but I wish he had more to say. I agree that its very difficult to compare apples and oranges (Harvard GPA to UMass GPA)--in this case because we don't have any good data for estimating the variance in GPAs at each college.
Also, this is funny. I found a treasure trove of law school admissions data that I'm going to mine for insights. One day they will appear on this blog (vis a vis medical school admissions).