Some blogs have thousands of daily visitors because they were there first. It is like carbonated drinks. Even if you make a drink that is much better than Coke or Pepsi, you are doomed to bankrupcy because they pre-empted you. And sure, even in the early days there was competition, and people like Kos, Atrios, Billmon, Drum, Marshall etc. were probably better than their competition, thus they are now deservedly the stars of the blogosphere. That does not mean they have managed to retain the high quality of writing that perhaps characterized their early years. Being at the helm of such a big blog gives the owner a sense of responsibility to his/her audience to produce something every day. It is also interesting how small the blogrolls are of the "Big Blogs" - they tend to only link to each other. It also appears they also read just each other, and have quit commenting on other people's blogs (if they ever did it). Thus, a knot in the network appeared, formed out of about a dozen or so Big Old Blogs that only link and refer to each other. This is the blog aristocracy.
Some blogs have thousands of daily visitors because the owner was famous before even starting a blog. Journalists like Adam Nagourney, Matt Yglesias, and Keith Olberman were immediate hits as soon as they started blogging. Sci-fi writers, like William Gibson, Greg Bear and David Brin would never have the kind of audience-size as they do if they were not famous to begin with. People with real expertise, who can do more than provide links to NYT and a couple of lines of personal opinion are also magnets for traffic. For questions about law, you go to Juan Cole or the new Posner blog. Science? Carl Zimmer, PZMyers, Saun Carrol and David Appel have made their names in science circles way before they started their blogs. Philosophy? How about Brain Leiter or Sahotra Sarkar? I am glad to see more and more experts blogging and attracting large audiences. It is important for widespread dissemination of information that it occasionaly gets "vetted" by people who are trained to evaulate a particular type of information.
New blogs have a harder time. It is New Coke. It takes some really good writing, a dose of rare expertise, and a novel way of thinking for a new blog to start penetrating the blogospheric consciousness. That is why Legal Fiction and Total Information Awareness are, for instance, gaining more and more readers as the time goes by. I have received quite a lot of nice e-mails recently, incidentally more for my mini-"expertise" on Lakoff's scheme and logical continuation of it, than for my real-world expertise in circadian biology. But it took a lot of shameless blogwhoring in the beginning to get off the ground at first.
While old Big Blogs are themselves centers of the Universe from which all opinion radiates, small blogs have a different strategy. Large blogrolls, lots of blogwhoring, commenting on each others blogs, linking to each others post - those are all strategies to gain one's visibility, with a consequence of new knots forming. These new knots are much larger than knots of Big blogs. Several dozens of blogs in each knot keep linking to each other all the time, and the knots get bigger and bigger, connecting to each other, forming a really extensive web which only tangentially includes the Big Old Ones.
Joining group blogs and blog alliances is another way the knots (or nodes, if you prefer that term) expand, each individual blog vying for increased visibility in ever greater competition. One new way of spreading the knots are Blog Carnivals. The original is The Bonfire of the Vanities (http://wizbangblog.com/archives/cat_bonfire_of_the_vanities.php). My personal favourite, of course, is Tangled Bank (http://www.tangledbank.net/), collecting posts about biology, nature and medicine (if you have a post like that, submit it to me until January 11th: http://sciencepolitics.blogspot.com/2004/12/call-for-submissions.html). Blog Tower is a collection of some of the best writing of the "small" blogosphere (http://mysite.verizon.net/vze7rlxx/bthome/). There is a medical carnival (http://izzy.typepad.com/undisclosedlocation/2004/10/grand_rounds_ar.html), a philosophers carnival (http://philosophycarnival.blogspot.com/), a Christian Carnival (http://mediasoul.typepad.com/mediasoul/2004/12/christian_carni_2.html), an "early modern history" Carnivallesque (http://worldupsidedown.blogspot.com/) and many others, including a carnival of erotic stories (http://www.nyhotties.com/archives/2004/12/carnival_of_sin_8.html).
Apart from Blog Tower, all the carnivals tend to bring together bloggers interested in a particular field, including the experts in that field. Is that going to result in "Departmentalization" of the blogosphere? Or is it just a natural process of organizing a complex system, so everyone knows where to go for what kind of information. It is useful to have all of your liver in one place and all of your pancreas in another - that way the nervous, immune and endocrine systems know what to do and where to send their signals. In the same vein it may be useful to be able to find all the philosophers in roughly one place, all lawyers in another, all biologists in yet another place, and all meta-bloggers (blogs about blogging) in another.
I bet people are writing their dissertation about this as we speak. I hope those dissertations get posted on their blogs once they get done and defended. It will be interesting to see how the system evolves in the future.