Once upon a time, before I was old enough to vote but old enough to pay attention to the evening news, there were Presidential Elections that people claim were swung in part by the television media folk calling the election long before polls had closed in Western states. Even people who accepted the statistical models that said those votes Did Not Count still thought it was bad form and that has shaped news coverage in succeeding elections. Also, closer elections have shaped news coverage in the last decade, but that's not precisely relevant to this particular post.
Which is basically about states that let you vote early. Like western states with very inclusive absentee ballot rules.
If you live out West, but your entire state (or, say, 60% of the previous cycle's voters) votes in the week leading up to the election, we might get a reverse early call: the results out West mean the vote Day-Of in Eastern states Does Not Count (much).
Not this time. This time, it's more a matter of the walls closing in on McCain.