Why would they all be at pain number zero? I'd expect them to be randomly distributed in all their traits unless specified otherwise. If I give them a mean pain of zero and a standard deviation of 1, there'd be no shortage of people with a pain level of 1,000,000,000,000. The same goes with any reasonable distribtion.

It's a thought experiment. The whole scenario is utterly far-fetched, so there's no use in arguing that this or that detail of the thought experiment is what we should "expect" to find.

As such, I choose the version of the thought experiment that best teases out the dilemma that Yudkowsky is trying to explore, which concerns the question of whether we should consider pain to be denominated all in the same units - i.e. 3^^^3 x miniscule pain > 1 x torture - in our moral calculations.

EDIT: in response to the rest of your comment, see my reply to "Unnamed".