Matthew Yglesias makes some great observations about the different types of questions during the Dem debate. Reporters were asking about politics, trying to evoke divisions among the candidates or to catch individual candidates in inconsistencies. Audience members asked about policies, often informed by experiences in their own lives. A glaring example was when an audience member asked what qualities candidates would look for in Supreme Court nominees, and the reporter changed the question to make it just about Roe v. Wade.
Yeah, I found Blitzer pretty annoying, but the whole distinction here is one of priorities. News reporters want fireworks, which make good copy. Professionally, they don't care who wins either the debate or the nomination. Audience members want to know which candidate is closer to their priorities and which could win, which is how they make voting decisions.
More on the Blitzer style from Digby.