There are a lot of high numbers out there yet only a little over a hundred spots for the incoming class. Let's look at it from WashU's perspective, if you were to choose how to pick one of those applicants how would you weight the following:
1)essays: mom, professionals, writing tutors can write those
2)grades: you can easily cheat, have an easy class, easy professor, etc.
3)activities: easy to embellish
4)MCAT: controlled environment, standardized across the nation, you either know it or you don't (and a good predictor for Step scores)
5)interview: you have the person sitting right in front of you, are they the real deal or not, are they fun to talk to, will they make a great addition to the incoming class?
Keep in mind the less you weight the standardized (MCAT) and "she's sitting right in front of me (interview)" things, the more weight you give to biased sections in the app. Perhaps that is one reason why WashU focuses on interview and MCAT?