IM overall is not a very competitive specialty. Thus, do people with just average board scores match easily in good IM programs like WashU and Michigan? or are these programs as competitive specialties like ortho, ophtho, rads, etc

Overall, obviously, the specailty is not competitive. If you want to do IM you can- the same doesn't hold true for those other fields. However, at the top places, you need similar stats, I'd venture, to match in competitive fields. UMich and Wash U are very prestigious programs and I doubt you'd get an interivew without some substance on your CV. I interviewed at UMich this year and everyone I was surrounded by was very, very qualified. As for the super elites BWH, MGH, Hopkins etc. the only friends of mine interviewing there are AOA, >240 Step I- anecdotal, I know, and someone is bound to contradict me, but from they told me, the people they interviewed with were equally impressive. I got rejected from BWH. Woohoo.