The Vote in Iran – Revisited

Yesterday I posted a chart showing that as Iran's Interior Ministry announced election results throughout the day, the winning percentage for Mahmoud Ahmadinejad had stayed almost eerily constant.  It seemed likely that in a genuine election there would have been a little more variation, so this looked like a piece of evidence that the vote count had been rigged.

It still seems likely that the vote was rigged, but the steady vote count apparently doesn't prove anything one way or the other.  Nate Silver plotted the 2008 U.S. election results using waves of states in alphabetical order, and he came up with an almost dead straight line, just like the Iranian results.  One of Andrew Sullivan's readers did the same with the results as announced every half hour through the night, and again the line was as straight as a laser.  So this is apparently a null piece of evidence.

But now I'm curious.  The Sullivan graph shows that by 7:30 pm Eastern time, when you have two data points, you could predict the final popular vote in the 2008 election with about 99% accuracy.  Question: would you get the same results if you plotted the last five or six elections?  If so, it means that most years we'll know with almost complete certainty who the winner is by 7:30 pm, exit polls be damned.  Can this really be true?