By demonstrable I mean we can point to 100-200 companies in a ten year period that took VC and had respectable exits. There are probably more than that, but there is a good sample size.

I agree that it is improbable, but still better than the lottery. My point was that there are lots of well known examples from the VC route, but fewer success stories in the 37 Signals mold. It also might just be that they are lesser known, but instead of berating the VC industry maybe they could turn their spotlight on exemplars in their model? 37S, Craigslist, Plenty of Fish, are there a couple hundred bootstraped web startups that they could point to?