Equating the "simulations" that we run and the "simulations" that Boström requires is ridiculous.
There's no reason to believe that the type of simulation required for this argument is even possible.
His argument is about as sensible as:
1) To a caveman, our technology would seem god-like
2) Technology is improving
3) There is no reason to believe that technology won't become more advanced over time
4) Therefore, god will eventually exist (or at least beings that we would identify as godlike).
There is no reason to believe that the potential power of simulations is unlimited. If there is an upper limit on how powerful a simulation can be, then his statistical arguments become meaningless. He makes some hand-wavy arguments about the potential power of computers, and the required capacity to simulate a human mind based on some quite questionable sources.