On the other hand, popular media that are not generally treated as art are rarely categorized into genres either. This suggests again that "genres" are particularly categories of approaches to arts that are used as a simple tool for producing popular rather than good works.
Simplistically, then, genre would not apply to blogs unless they are considered art. However, as even the writer of this entry points out, genre is applied to television and I think most of the time, we wouldn't equate television shows with something like sculpture.
From this Introduction to Genre Theory (which I've only skimmed), however, we find a way out of this dilemma.
How we define a genre depends on our purposes; the adequacy of our definition in terms of social science at least must surely be related to the light that the exploration sheds on the phenomenon. For instance (and this is a key concern of mine), if we are studying the way in which genre frames the reader's interpretation of a text then we would do well to focus on how readers identify genres rather than on theoretical distinctions. Defining genres may be problematic, but even if theorists were to abandon the concept, in everyday life people would continue to categorize texts.
I think that there are genres on the web. And, a quick google search reveals there is a little research out there on such things. One of the more interesting articles was this article. However, much of the research seems oriented toward enabling better searching and not analyzing the development of genres. Switching search terms from the general genre and web to genre and blogs lead to more interesting results. I'm sure a thorough library search would yield even better results, but I don't think that's going to happen at the moment. Maybe someone out there has some better ideas. It seems, too, that subgenres of blogs are constantly shifting and that the conventions of blogs are constantly shifting perhaps as a result of what people want and expect from blogs. It is certainly fascinating.