When There Isn't A National Primary, National Polls Don't Matter

Mark Mellman gets it:

"If there was a law requiring relevance, national polls would be illegal."
-- Pollster Mark Mellman, quoted in Salon, on polls showing Sen. Hillary Clinton leading the Democratic race.

For some reason or another, national polls are regurgitated and promoted far more than polls that actually mean anything - those in early states like Iowa, New Hampshire, and South Carolina (though, given undecided rates and how hard caucuses are to poll, even those are of limited value this early on). At some level the media is unable to fathom that the entire nation doesn't vote at once in a presidential primary; if it did, then this obsession with national polling would make sense, but in a system where an Iowan's vote is worth orders of magnitude more than a Californian's, it's just a waste of time.
If you want proof of this, look through PollingReport's old 2004 national primary polls. A poll taken from October 27 to 29 shows Dean, Lieberman, Gephardt, Kerry, and Clark, in that order. An early November poll shows Dean, Clark, Gephardt, Lieberman, then Kerry. Sharpton beats Edwards in both. Suffice it to say, that's not how the primary turned out.