I don't generally recommend kos, he's kindof overplayed and a little too tribal. Most of the time when I read him it's to get the opinion of someone who is steeped in liberal politics, just to see what the conventional liberal blog wisdom is. But every once in a while he says something insightful enough to transcend the daily grind of liberal tribalism.
Frankly, I don't think that Barack Obama is going to suddenly turn into John Edwards. I think that his campaign has studiously avoided this third rail because of the backlash that they fear from the media and other powers that be. In the same way that (serious!) conservative candidates cannot come out against evolution and expect to win mainstream elections, serious liberal candidates cannot come out railing against the excesses of the rich. The system does not permit it, it's too far outside the norm. See also: Ron Paul, Howard Dean.
The question is, has the campaign studiously avoided this sleeper issue because they don't believe it's relevant, or because they think it might sink them electorally? That is what's actually interesting about the "bitter" comments. Is Barack a populist in mainstream clothing? I would argue that a real firebreathing populist in the White House would be far more disruptive and historical than either a moderate woman or a moderate black man, and thus will face greater institutional opposition than either.
In any case, I'm excited to see what happens.