I will also be attending UWSOM this Fall 2013 (go class of 2017 woot woot!).
I think UW's lower scores compared with its peers really does have to do with its interviewing process.
Basically, you're in a room with 3 admissions committee members (2 faculty or students from a general pool of admissions members and 1 executive committee member, the member who "advocates" on your behalf to the entire EXCOM). Everyone can see your AMCAS and your secondary essays, but only the EXCOM member can see your MCAT scores and grades. I think this is really helpful in eliminating biases based off your scores and grades.
This system makes UW's interviews really quite different from the one-on-one faculty interviews at most schools. It also makes the interviews quite challenging and thought-provoking as well.
From my interview experience, they asked me questions about my experiences that I had never been asked before in my interviews at other schools. UW also LOVES scenarios and role-plays about ethical clinical issues and healthcare reform. This is not necessarily to put you on the spot but to evaluate your thinking process (are you able to think critically about these issues? are you able to respond appropriately, like a physician?)
After your interview, the three faculty members write reviews and evaluates you and then the EXCOM member presents those evaluations to the full EXCOM.
So, UW cares less about GPA and MCAT and cares more about the applicant's potential to be a clinician foremost and a researcher second (however, UW's research is seriously no laughing matter. UW research has a HUGEEE presence in the Seattle area that is unchallenged for miles in all directions.) UW actually has the second highest TOTAL (so all schools in addition to the school of medicine) highest NIH funding (after Harvard): I think the figure was 700 million. O_O
Coming from a top 3 university, I also was slightly surprised by UW's GPA and MCAT averages but I realize that just because your MCAT was a 30 doesn't mean that you'll be any less successful than a medical student who had an MCAT of 39.
And to brag about UW even a bit more: UW is really unique among medical schools because it is seriously the ONLY REGIONAL medical school in the US and probably in the world. That means that there are medical school campuses affiliated with UWSOM in Alaska, in Idaho, in Montana, in Wyoming, and in Pullman and Spokane (the Washington state university campuses). The strength of the WWAMI system really shines during clinical year, because you don't just have the option of doing rotations in Seattle hospitals but literally all across the region, like some 200 clinical sites JUST to do clinical rotations. How friggin awesome is that? =)