Don't you think that the selling of $23,000 usability testing workshops might constitute an incentive for him to push for more hands on usability testing rather than the blind acceptance of his findings?
But you said that he is a powerful proponent for low-cost, self-run tests... and he's not, really, as I pointed out. Lukewarm at best, perhaps.
Meanwhile, why do you think he doesn't recommend testing for differences when he makes his announcements regarding findings? Or even mention that they vary?
This is just pure speculation, but it seems as if he's more concerned with sounding authoritative -- so people hire him -- than pointing out the ambiguities in statistical usability research.