Yes, I've read Bostrom's paper[0], but he misses a key point: the number of rational beings in each simulated universe may decrease exponentially. If, on average over all universes, each rational being simulates only 0.5 rational beings during his or her lifetime, the total number of simulated rational beings would be exactly equal to the total number of unsimulated rational beings, making it equally plausible that we are in the root universe or one of the simulations.
The possibility that rational beings diminish in number exponentially as universes are simulated seems not only plausible, but likely given the nature of the simulations necessary to replicate our universe in all its detail.