I think blogs are less their own media than a huge letters to the editor section. For example, without blogs we wouldn't have seen PZ Meyer's huge correction to some wacky article. You often see people replying and giving their own commentary to the news using their own expertise. They aren't being reporters themselves but instead commentators. This new group of commentators allows folks who a)are busy being experts in their fields, but never get called onto TV because TV shows are too busy putting on some random kook for balance b)people who couldn't get into journalism because they needed to eat/systematic discrimination against them to really correct the news and bring new views into it.