The notion that the Internet is a more reliable source of information because of diversity needs to be approached with a healthy degree of skepticism. Particularly the blogosphere--it's provided individuals with a voice, but the response mechanism you highlight as a means to validate the truth of a particular blogger's assertions really isn't a validation mechanism. It's simply an endorsement method, a popularity poll, generally, and that's not the same. At every blog I've ever visited, the "atta boys", "dittos", and "yeah, me too" comments vastly outnumber the challenges. Blogs propagate memes by increasing their mass, but rarely their quality.
You know you can go out and find blogs about anomalism, the flat earth, every religion under the sun, and, generally, just about every idea that's popped into somebody's head since blogs were invented. And you can be just as sure that every such blog has accreted a certain number of followers who share that belief. I think we're approaching a billion Internet users--what are the odds that at least a few dozen will subscribe to any particular belief?
Blogs form networks of like-minded individuals, and such networks are easily manipulated. We see dramatically in an election year how memes can be injected into the blogosphere and propagate at the speed of light, with thousands of bloggers repeating verbatim some party line, each one pointing to the others as proof that some assertion just has to be true. Dare I use the phrase "cybernetic circle jerk"?
On the blogs, my comments and arguments on facts usually go smack under the story, to be judged against the main story. Others can add comments under mine. All are visible to everyone else.
And this differs from a BBS how? Blogs may be newer and thus have some novelty value, but if we can't determine the truth in this format, why expect that the virtually identical blog format will reveal truth?
Let me go further, and observe that a BBS is a more egalitarian form than a blog. Blogs are owned by one individual, and that individual starts every discussion; other participants are in an unequal subsidiary role in which they only respond. They're free to set up a counter-blog, but it's somewhere else--discussions are compartmentalized around loci of agreement. At least here the arguments and counterarguments face each other across the table.
Blogs are a good thing, on balance, but they require a huge dose of skepticism. They're not immune to manipulation, and they're at least as likely to produce a memetic stampede as they are to separate wheat from chaff.
We haven't reached the Promised Land yet, I'm afraid.