I wonder how much this has to do with the decrease in actual science being blogged on science blogs?
It used to be all science all the time, with a few bits and pieces of other material tossed in for seasoning and leavening. That's why I started coming here.
Now it seems to be the other way around. For just two examples, I used to read Pharyngula, can I say, religiously?! Now I read it hardly at all because PZ doesn't typically blog science any more. And I fully support his atheist stance, but I don't come here for atheism, I come here for science. I used to read Grrl Scientist regularly, but she, too, has migrated to other topics and blogs hardly any science.
Those who do routinely blog science - such as Ed Yong - seem to be moving on to Discover blogs. I'm forced to wonder what that says about "Science" Blogs.
It's true that we have recently lost some of our more heavily science-themed blogs to Discover. However, while I can't speak to how the concentration of actual science blogging has changed over time here, I can say that there is still quite a bit of science being written about on ScienceBlogs! I just took a look at the first page of the Last 24 Hours feed, and from a quick examination, here are my findings:
Out of 23 posts, 5 were purely scientific (and 3 of those were about "hard" science). However, an addition 10 were about science-related topics, and only 8 were not about science at all. I'd say that's still a pretty high concentration of science!