Maybe it's just me but on countless occasions I've wrongly voted to close after misreading the question (oops). Either that, or the OP has modified their question following a comment to bring it in line with the types of questions allowed in the FAQ.
If you're on 4 close votes with no way to undo and someone comes along and decides ooh, 4 votes, I'll add my 5th one... without really thinking, you then have to go back through the whole reopen process again. I doubt this happens very often to be honest but it would still be very useful if there was a way to undo your own vote to close.
Is there a way to undo my own vote to close for a question?