Slate has a breakdown of the different pollsters and how well they predicted the election. One point near the end talks about the effect of using automated polls vs. live pollsters.

How did the robots largely beat the humans? For starters, they aren't robots. They're recordings of human voices. Pollsters who use this technology argue that the uniformity achieved by automation—every respondent hears the questions read exactly the same way—outweighs any distortions caused by people hanging up or lying to the recordings. They also argue that the interviewers who read questions and record answers in "human" polls are all too human. A human poll may bear the name of a major newspaper or television network, but the interviews are usually "outsourced" to a company you've never heard of and conducted by whoever is willing to make the phone calls—which sound a lot like telemarketing—for modest wages.

Robots have one additional advantage in this particular election. People are less likely to lie to a robot than a human. I have said before that there was probably a lot of people who voted for Bush but didn't want to admit it, even to an anonymous pollster.

Further evidence that I was right can be found in the article.

Historically, last-minute undecideds have broken decisively for the presidential challenger. Based on this pattern, Gallup allocated 90 percent of its undecideds to Kerry, lifting him into a tie with Bush at 49 percent. TIPP made a similar bet on the 4.4 percent of voters in its final survey who said they were still "not sure" whom to vote for. TIPP allocated 61 percent of this group to Kerry and only 34 percent to Bush.

Oops! According to exit polls, Bush got 46 percent of those who made up their minds in the last week of the campaign and 44 percent of those who made up their minds in the final three days. TIPP got it wrong, Gallup got it very wrong, and Slate's vote-share formula got it very, very wrong. Who got it right? Pew again. In its final report, Pew predicted that undecideds "may break only slightly in Kerry's favor." With 6 percent of voters undecided in the week before the election, Pew added 3 percent to Bush's total and 3 percent to Kerry's.

I'm guessing that a lot of these "undecideds" knew that they were going to vote for Bush but didn't want to admit it.