I think it's definitely worth considering the difference between the media industry, and journalism as two distinctive practices which are sometimes, but not always linked.
However, I will say this: the vast majority of what is discussed on blogs still comes from traditional media outlets. Traditional media outlets have the funding to allow them to have foreign correspondents, to undertake investigative journalism and to expose newstories to far greater attention than independent bloggers do.
And the problem is that business model is collapsing, and when it does, bloggers are not going to be able to jump in the breach and perform the same kind of service.
Blogs seem to perform best as op-ed mills for their respective author(s). Which is all fine and well, so long as the respective authors know what they are talking about. But guess what? Many of them don't. The most popular political blogs in the US are not run by political scientists, talented analysts and former strategists - they're run by rabid partisans with too much time on their hands. Poli Sci blogging is a niche interest, and a frequently underrepresented niche at that. You know who is overrepresented in political blogging? Office workers and academic lawyers...and most of the latter never even discuss law! People who've mastered the art of being verbose and obsessive about news stories, but not necessarily people who have any relevant knowledge on the topic at hand.
Science blogging is in a good place, I agree, and that's because the sciences themselves are in a far healthier position than most of the rest of what is considered news. And that the people who are running science blogs know what they are talking about, because if they do not, other science bloggers descend on them like a swarm of locusts and leave no-one in any doubt that they do not know what they are talking about.
Political blogging isn't like that. If a blogger is wrong, and you try to tell them that, you'll end up being blocked most likely. If they even take notice of you, which they probably wont since the influential blogs get a couple of hundred comments per entry. And if you tell them they're wrong and you're from an opposing political team, or perceived to be, well, prepare to be eviscerated. This is because Politics Is The Mind-Killer, as we all know too well. Political Scientists can resist this (partially at least) through use of statistical wards, but everyone else is screwed.
Professional journalists are likely depressed by the state of the media industry, and every metric says that is pretty much the right position to take. The media industry is depressing. New journalists are likely to be excited by the potential of blogging, Twitter, social media etc. And the potential for it to be very powerful is there. But at the same time, the potentials of those tools are going to require money for anything more than a cursory analysis. And that's where journalism and the traditional media meet. Those independent websites who do try to do proper investigative journalism without the backing of the media are few, and tend to be in a constant state of fundraising, for emergencies.
That's the reality of the situation, as it currently stands. Potential, but without funds. People prefer free news, and blogs allow for that, but the news has to come from somewhere, and eventually there is a cost involved, which is what is undermining the traditional media. It's an untenable situation in the long-term. Something will have to give.