OK. If that Behind the Eclipse was accurrate, then I was right. Arthur does not steal powers leaving the othe rperson void of abilities unless he chooses to. That BtE said he was using the Haitians mind wiping power on Hiro. That would mean he had to copy the Haitians power in the past, but he obviously didn't completely steal it from him.
Thus it is also completely plausible that Arthur's telepathy is indeed from Maury.
As to Hiro's thinking he is 10, that seems clear now. Arthur was in the process of completely erasing his mind but then got distracted by the eclipse painting. So he only erased everything back to Hiro's memories at age 10.
Once again, if people stop having knee jerk reactions and flipping out, being patient shows that many of the "plot holes" are easily explained.