37signals had an obvious business model and revenue stream on day one.

It's pretty much the perfect example of the difference the author is trying to draw: google and twitter were highly experimental ventures with no visible means of support in the early days. 37signals was explicitly a paying business.

I'd say 37 Signals fits the point of his article. He's not saying that Midwestern startups can't succeed, but rather the mentality grows startups cautiously, with less investment capital and slower growth.