At your top 15 program was EVERY class curved down? For example, if the average on a particular test was a 90%, does a 90% become a C+? This is the only way your contention would make sense to me. Do all of your classes utilize a bell curve or are any other methods used to curve classes (e.g. grade forgiveness)? Not all of the courses at my state school even had a curve. It makes your argument irrelevant for those courses. For the classes that did curve, the average was still a C, and only the top ~5% end up with an A. Those top ~5% tend to be pretty smart and diligent workers, and if they were at a top 15 program, I'd bet they would still be earning As... Food for thought, most of the students who consistently had those grades at my school had exceptional MCAT scores (33-39).
P.s. There are differences in rigor between majors and classes (with different professors) at my institution. Some professors are easier than others. Are all majors, classes, and professors created equally at your institution (i.e. unanimously more difficult than state school classes)?
P.S.S. I recall comparing the tests for several of my classes with those on MIT open courseware, way back when taking those classes, and not noticing significant differences in rigor. I feel that this supposed difference in rigor is grossly exaggerated.