I haven’t read through all the pages of posts since I last saw the thread, but the discussion of B in AP vs A in regular seems too hypothetical to have much practical use. How does a student know whether he is going to get a B or an A in an AP class until it is too late to easily drop out? Personally, I found it easier to get A’s in AP and DE classes than regular HS classes because the material was more interesting to me, which probably largely relates to taking higher level classes in fields I was more passionate about and taking regular classes in fields I was less passionate about.
I think the more relevant question is what percent of students with sub 4.0 get admitted. If you instead only look at the % in entering class, you have no idea whether the high % of the entering class with 4.0 more relates a large portion of the applicants having a 4.0 or the college strongly favoring 4.0. Some stats for Princeton are at https://admission.princeton.edu/applyingforadmission/admission-statistics . Their admit rate by GPA is below. Also note that there is no control for a variety of other relevant admission factors that are correlated with GPA, so we are also seeing effects of additional admission criteria that are more likely to occur in the 4.0 GPA applicants such as better scores, LORs, major awards, etc.
4.0 – 9% Admit rate
3.9-3.99 – 8% Admit Rate
3.8-3.89 – 6% Admit Rate
3.5 - 3.79 – 3% Admit Rate
Below 3.5 – 2% Admit Rate