I think he is just disappointed at the media. After the catastrophic failure that was the Iraq war, everybody was just pointing the finger to somebody else and continued the same way.
While Stewart was relentless against stupid crap like Crossfire on CNN, its nothing compared to the incredible stupidity, they show now. Blizzer is just telling people what he sees on TV, because they got nothing. No insides, no real discussions, nothing. The fill the void with pictures and describing pictures.
Journalism and politics in the US is in such an abysmal state, that it hurts him to even make jokes about it. You see it more and more often and I think, it would have killed him inside, if he would have continued. The look on his face after the interview was incredible, it really hurt him how media tries to swindle itself out of this again.