I'd be quite surprised if Amazon hires less than 3,000 software engineers a quarter. U Michigan may be a good or great engineering school but if it's an hour away it rounds to part of the national market.
I went there, along with several of my friends. Most of them now work for Amazon, several in the extant Detroit office and commute there from just outside Ann Arbor. You'd be surprised at how easy an hour commute is in South-east Michigan, esp. compared to Cali or Jersey traffic.
Stanford and SF are a similar distance, and I don't think anybody would say that Stanford "rounds to the national market" for SF companies. I certainly know plenty of U of M grads who have ended up in Detroit, so I suspect your theory needs some work.
