The issue with a string of 4's is that so many kids will have all 5's or mostly. Including in tough courses related to the proposed major. As standardized tests, AP's, like SAT and ACT scores, are a mark of how well the student learned the coursework and how motivated he/she was to do well on the test. Ie, not just how the kid did with that hs teacher. But, as someone pointed out, the general review is holistic, so you could have a case where 4's are outweighed by experience and personal characteristics. If the rec is a science S2 and there isn't one, chances are someone will note that. You have to remember the competition is fierce.