Scott Winship has more up on the Prospect website about the ideological proclivities of the netroots. It occurs to me reading his article that it's worth keeping in mind that what "the netroots" is is, at this point, almost certainly something of a moving target.
The thing about the internet is that, at the moment, it's all a relatively novel technology and, consequently, has very uneven penetration throughout the country. In particular, blogs are -- as of today -- both a very high-profile phenomenon and a rather narrow one. Lots of people read some political blogs, and we've reached a point where all professional political people -- be they journalists or operatives or politicians or what have you -- know what they are and know something about it. Consequently, they have some influence. But at the same time most people aren't actually engaged with the political blogosphere at all, just as most people don't know how to use BitTorrent, don't understand how Wikipedia works (as witnessed by the fact that The Atlantic has a long article laying it out), have never used Voice Over Internet Protocol, and despite their burgeoning popularity have never visited YouTube or Flickr.
When you think about this stuff outside of politics, the common assumption is that just like the basic technology of email and online shopping, these things will spread over time. Telecommunications firms assume that someday just about everyone will use VOIP and that the related Video Over Internet Protocal technology will become extremely important as fiber-optic connections spread. Everyone will, someday, start posting their photos to Flickr and check out amusing things on YouTube, or else those sites will come to be overshadowed by something similar but better.
Blogs are probably the same way. At the moment, they have an "early adopter" demographic -- whiter, richer, better-educated than the general population -- and, consequently, the class of progressive blog readers has a different ideological caste than the general class of people who usually vote for the Democrats.
Over time, though, one would expect the demographics of the blog audience to converge with the overall demographics of the population. There was a time, after all, when the demographics of people with cable television was very different from the demographics of the population at large. Similarly, there was a time when the demographics of people who'd ever used a computer was very different from the demographics of the population at large. Over time, though, those technologies -- like anything else -- spreads over time and becomes normalized. Blogs will probably follow the same trajectory and the political "differentness" of the netroots should abate consequently.