I've heard a lot of people saying this, but the conclusion is not exactly accurate in its explanation. They aren't "drawing support from McCain" because he didn't really have it to begin with. It only appears that way because of a question that has no basis in reality. They aren't "adding in" the other candidates to the second question; they are actually "taking away" candidates in the first. While it seems like the same thing, it really isn't, because one is based in reality, the other is a hypothetical.

Asking "If the election were today; who would you vote for?" and "If the election was today, and you could only vote for Obama or McCain, who would you pick?" are two totally different questions. One is an accurate assessment of how things are now if the election was today, the other is an assessment of a hypothetical election. I feel the two person polls should never even be asked. They give nothing but a false representation of the vote.

Nader isn't pulling votes from McCain, because McCain never had them. Most Nader votes are anti-Obama votes. Democrats that are angry at Obama (PUMA's, etc) that won't vote for Obama. So when restricted to an Obama/McCain choice they are anti-Obama so "vote" for McCain. But the ballot isn't restricted, so McCain really doesn't have their support, it's just an appearance of support because of the faulty question.

Barr votes are mostly right wing anti-McCain votes but are more anti-Obama than anti-McCain. So again, when given the faulty question of just Obama/McCain they go with McCain. But again, the ballot isn't going to be that faulty two person match up, it will be all four in many states (and even other parties too). The multi-person polls are far more accurate picture of the support because they resemble the actual ballots.

The fault in the media's argument that McCain is losing support when adding in the other two candidates is that you can't look at it in a bubble like that. They are using a hypothetical match up to give him unrealistic support that he really doesn’t have, then trying to say that he’s losing that support by those candidates being there. It gives the impression that if those third party candidates lose support towards election day that it all goes towards McCain. That is the real fault... because they are suggesting that the Nader "anti-Obama vote", if it diminishes, is going to go with McCain. Some might, but some of those disaffected Dems may return to the flock and vote Obama... or some may just stay home.

The 2% increase in undecided is also "anti-Obama" votes. When given the choice between Obama/McCain they go against Obama, but when given 3 choices and Obama they become undecided. They are still anti-Obama, but aren't "for" anyone when given a choice. They are clearly not pro-McCain at this time.

You can’t say what is going to happen with these people, so trying to give that support to anyone is just a guess at best. But the media is trying to put that support in McCain’s corner with these poor polling questions to make it a tighter race.

So the most accurate situation you have is:
46% Obama
36% McCain
3% Barr
3% Nader
10% Truly Undecided
2% Undecided Anti-Obama

Compare those numbers of support to other polls that ask different questions on issues, and they line up a lot better than what the faulty two person polls display.