You always have to take rankings like these with a grain of salt, because measuring web traffic to a website is a very imprecise science. I always laugh when I hear somebody talking about their Alexa rankings as if they were some kind of definitive guide to rankings on the Internet. In a general way, Alexa rankings will get the *relative* popularity of a website right, i.e. "Slashdot" is far more popular than "Stand Down," but in terms of exact rankings, Alexa is as imprecise as other methods of measuring website popularity.
Another problem with the rankings at Right Wing News is that the author of this ranking is obviously unfamiliar with a bunch of leftist and progressive blogs. Of course, as he points out, it's pretty difficult to determine what is a "blog." Infoshop News is technically a weblog--I consider it to be a news service--though it doesn't appear in these rankings (it would come in around #15, with an Alexa ranking that's in the range of 37,000 to 42,000).
The interesting thing about these things is that one always learns about new websites that are out there.
Chuck0