I don't know if this rises to what Michael Kinsley calls a "gaffe" (ie., when a politician accidentally utters the truth), but the Obama Haters in the blogosphere are having a field day with what can only be interpreted as a willful misprepresentation of the statement in question. It is a matter of fact that half the country was disinclined to vote for the Democratic nominee in 2000 and 2004, just as the other half was disinclined to vote for George Bush. There is nothing in that statement that blames the party standard-bearers for the polarization (neither was even mentioned by name), nor can it even be remotely interpreted as a criticism of the Democratic Party.
It's just a fact that Democrats have participated in the last two Presidential elections facing a divided country, where its message fell on deaf ears, and were either defeated twice, and/or put themselves in a situation where they could be screwed twice by malevolent Republican votecounters. Senator Obama is simply stating that rather obvious fact, with the implication that maybe such polarization is not a guarantor of future electoral success for The Democracy. Whether he's the one who can expand the electoral base of the party is another question entirely, but it's not inappropriate for him to base his case before primary voters on that issue. Kos and Digby really should know better.