Over the past century, media has enjoyed a period of relative profitability. Newspapers, radio stations, television stations, and so forth were all able to do their jobs and generally make money. I think that era is ending. Blogs aren't themselves the downfall of the existing business model, but they're a harbinger of things to come.
GM Vice Chairman Bob Jutz now runs a blog called Fastlane on behalf of his company and he doesn't expect the blog itself to make money; he just hopes to create synergy (argh!) between his customers, critics, and company. And judging from his energetic comments section, it looks like he's succeeding. He talks honestly about his products, and in one location even praises Honda interiors and holds them up as a target that GM is aiming towards, but at a lower price point. That's what people want to know about, and that's what you'll never hear on TV.
I doubt newspapers, television, and radio will remain profitable for very long. I doubt they'll disappear, but I wouldn't be surprised if they move towards a more blog-like business model of losing money in exchange for increased mass communication -- a sort of loss leader. Maybe I'm wrong, and maybe advertising dollars will continue to fund the sytem we've got, but it's hard for me to imagine it. Another alternative is the subscription model that the emerging satellite radio industry is using -- but as newspapers have long known, subscriptions alone can't support mass media.