A question for polling geeks

This Josh Marshall post raises a question that’s been bugging me for the last 48 hours:

The final FOX news poll — with calls on Saturday and Sunday only –has Kerry over Bush 48% to 46% among likely voters. Among registered voters it’s Kerry 47%, Bush 45%. Among those who’ve already voted, it’s Kerry 48%, Bush 43%. (emphasis added)

Here’s a more in-depth story by Dana Blanton on Fox’s results, which notes, “about one in five voters report they have already voted by early or absentee ballot, and these voters break for Sen. Kerry by 48 percent to 43 percent.” I can’t find that figure anywhere in Fox’s .pdf report of the results, but there it is. Here’s my question — this confirms other reports I’ve heard saying that the early vote favors Kerry [But see the update to this post below–ed.] So what does this mean for the election? There are three possibilities:

1) As in 2000, the polls for Election Day are missing turnout and early voting, and so the final vote tally will mirror the early voting and Kerry will win handily; 2) The early voters are disproprtionately likely to vote for Kerry so they have no bearing on the final outcome; 3) The polling of early voters relies on too small a sample and should be ignored.

Most cognoscenti seem to assume (2). My question is, why? The one argument that makes sense to me is that early voting is a sign of intensity of preferences, and the ABB vote is more intense than the ABK vote. UPDATE: Stop the presses! CBS News also has early voting results — but they have Bush beating Kerry!

Early voters split about evenly, one-third each between Democrats, Republicans and Independents. They are a bit older: one-quarter are 65 or over, and eight in ten are above age 45. President Bush holds a lead among them (51% to 43%). (emphasis added)

Let’s take a moment to allow the heads of those obsessed with media bias to explode at the thought that FOX has a poll favorable to Kerry while CBS has one favorable to Bush. However, the large contrast between the CBS and FOX results lead me to think that the answer to my original question is actually (3). One final question — the Fox result has 9% of voters voting for someone other than Bush or Kerry, and the CBS result has 6% of voters doing that. Who else are they voting for besides Nader? ANOTHER UPDATE: Over at Tapped, Garance Franke-Ruta has early voting numbers for Florida (a third of the vote cast; 51 to 43 Kerry) and Iowa (a quarter of the vote cast; 52 to 41 Kerry). However, Franke-Ruta seems to buy hypothesis (2) — early voters are more likely to go for Kerry. Link via Kevin Drum, who offers a hypothesis on why this might be true: “memories of Florida combined with news of Republican efforts to suppress voting have probably motivated Kerry voters to vote early in greater numbers than Bush voters due to their distrust of the voting process.”