It's accurate but doesn't prove what it seems to prove to the amateur eye. Read the whole thing. Money quote from a comparison with the last US election:
Ignoring votes for minor candidates, Ahmadinejad won a high of 70.4 percent of the votes in Wave 1, and a low of 62.3 percent in the votes newly added in Wave 6. By comparison, Obama's share of the newly-added votes in our experiment ranged from 56.4 percent in Wave 3 to 44.7 percent in Wave 4. That's slightly more variance than we saw in the Iranian results but not much.
To be clear, these results certainly do not prove that Iran's election was clean. I have no particular reason to believe the results reported by the Interior Ministry. But I also don't have any particular reason to disbelieve them, at least based on the statistical evidence. If Mousavi truly did have the support of a majority of Iran's citizenry, the best evidence we will have of that is what happens in the streets of Tehran over the next days and weeks.