My reading of the main argument here is that human theories are more likely when simple, not because of any fact about theory-space but because of the nature of humans' theory-generation process. In particular, theories that aren't correct acquire elaborations to make them give the right predictions, a la epicycles. This requires that theories are more likely if they can make correct predictions without lots of elaborations (or else theories with epicycles would be correct as often as those without). But in order for this rule to differ from Occam's Razor, we need to be able to decide what's the core of a theory and what's 'elaboration', so we can penalize only for the latter. I can't see any way to do this, and the author doesn't offer one either. And when you think in a Turing-Machine type formalism where hypotheses are bit strings representing programs, separating the 'core' of the bit-string-program from the 'elaborations' of the bit-string-program doesn't seem likely to succeed.