It wasn’t that long ago Northwestern and most of the others mentioned had EA and not ED. If I read their web site correctly Tufts can longer “Tufts” students since it is ED1 and ED2.
So yield protection in EA moves on to other schools. My point really is ED seems (to me) to be much preferable from the university’s perspective (given the large number that have moved that way this doesn’t seem crazy). The model of EA and trying to predict the small percentage who will actually come seems a much more challenging one. I agree a university will act in its own interest. My comment is really that I’m having trouble seeing the advantage to a university of EA over ED.
And one nit, I don’t think you can say Tulane ends up with a huge percentage of the kids they actually want when 22% offered admittance enroll. I do think you can say they feel that they achieved the best class for Tulane that they thought they could. I don’t mean to pick on Tulane here. My comment applies to all EA schools.