You're right, though, to hint at a certain type of media bias in blogging. It is the bias of the alternative media in general, believing its own declarations of authenticity, devolving into a smug superciliousness. Read any city's City Paper and you'll get a stale whiff of the last time a medium got too self-satisfied. There is the democratizing effect of cheap internet publishing, which allows for anyone to rebut anyone else. But obviously if I set up a blogspot site tomorrow because I disagree with an estabished site like Sullivan's Dish, the only way it'll get any serious eyeball is if Sully himself mentions it. This means that, as in any other medium, there will be an ivory tower effect. On the positive side, it will likely be a more meritocratic tower.
There are exceptions to any rule. There are plently of banal, NPR lefties out there, as the Dean-blogging phenom suggests. (But, again, it's a movement thing, a virtual Kumbaya session.) Then there are some straight up Republicans out there, too. Predictably, though, they tend to be of the fiscal conservative variety, not the moral majority variety. Not many blogs took to Judge Moore's side in the Ten Commandments hoopla, except as an intellectual exercise on the merits of strict constructionism. (Modestly ends post by pointing to self.)