These polls are like the “experts” that pick who the best players are in the upcoming NFL draft (to get in the spirit of the NFL draft tonight). They are nice and fun to talk about. But overall, meaningless and require time to play out the truth.
At this time in the election cycle for 2008 Rudy Guiliani and Hillary Clinton were the clear front runners. What does that tell you about speculating who is going to win the nomination at this point?
No two election cycles are the same. In 2000, George Bush was the frontrunner, and was never really challenged until McCain won convincingly in NH. Bush obviously came back strong in SC, sealing McCain's fate.
In 1996, Dole was the long-time frontrunner, and no one ever really challenged him, either in the polls or in the primaries themselves.
Had Clinton taken Iowa a bit more seriously, she very well may have won the nomination. Also, while Clinton was the early frontrunner, she also suffered from incredibly high-negatives. Those usually catch-up to you.
The 2004 Dem primary probably most closely resembles this GOP primary - a big field in which several candidates enjoyed almost 20% support, with Kerry, Edwards and Dean flip-flopping for control in the months leading up to the first primary. In the end, the winner came from those three long-time front-runners - Kerry.
Primary voters - the ones who actually decide the elections, which aren't usually the most political of the primary voters - are myopic. They tend to see things solely through the lens that the media creates for them. Right now, that lens is focused on these three guys, and that will be tough to overcome for the people in the back of the pack. While anything is possible, it's just not likely someone will come from way back. Even though McCain did in 2008, it' important to remember that McCain also was wildly popular with Republican-leaning independents, he had very low negatives (unlike Romney) and at one time he had led all comers earlier on.