Wow. I'm surprised at your need to rain on someone's parade. For your information, that mere 3,000-4,000 pool of applicants represents the finest applicants that exist in any given year. That's because most people think it's a waste of time for them even to apply. It's a self-selecting group. So to be among the select group of people who receive an interview from WashU is seriously impressive.
And to assert that they merely cherry-pick high stats among their interviewees is patently incorrect. If you get an interview--at any school--then you are clearly competitive in their eyes and they want to learn more. If they just discarded lower scores among their interviewees, there's no reason to interview them in the first place.