After Public Enemy's 1987 Nation Of Millions album proved samplers could rock harder than guitars, a lot of kids in England sold their guitars and bought samplers. In 1988, house music arrived in England, and a whole ton of kids had these samplers just sitting there ready to rock. Dance music and sample-heavy mashup bands (like today's Girl Talk) took over the British music press, and you couldn't open a Melody Maker or an NME without reading that rock music was dead forever.
Sample music spent a lot of time stealing riffs and soundbites from rock, and rock changed as a result, but it didn't change that much.
Blogs are going to kill mainstream news the same way that samplers killed guitars. Turn on CNN, you see bloggers where you used to see newspaper reporters. What else will change? Nothing. Blogs repost mainstream media news the same way dance music remixes every new hit track. If you're a band, your five minutes of fame will be retweeted on the dance floor live and in real-time by the best DJs on the blogosphere.
Ecosystems change, but kings remain kings.