If you're supposed to be some pious dude and then people find out you've been masturbating all over the place it may cause your followers to question your teachings. I guess that's what the government was hoping.
But it wouldn't surprise me if Osama beat it and bonged. Dude had kidney failure, plus he's a charismatic leader of an "underground" movement (like Koresh or Mormons) and those guys love to fuck and smoke weed.