Try this: do a search on "blog" with Google and see what happens. You should get the most important blogs, right?
Obviously, sites like Blogger and BlogSpot will appear in that list. You can also bank on actual blogs like Wil Wheaton and Dave Barry showing up somewhere in the top ten. But this is where things fall apart a little, at #6 --even if you limit Google to the last seven days-- is William Gibson's blog. Now, I'm sure it's a very nice blog that deserves high ranking. But here's the problem: he stopped blogging as of September 12, 2003:
Time for me to get back to my day job, which means that it's time for me to stop blogging. I've found blogging to be a low-impact activity, mildly narcotic and mostly quite convivial, but the thing I've most enjoyed about it is how it never fails to underline the fact that if I'm doing this I'm definitely not writing a novel – that is, if Imm still blogging, I'm definitely still on vacation. I've always known, somehow, that it would get in the way of writing fiction, and that I wouldn't want to be trying to do both at once. The image that comes most readily to mind is that of a kettle failing to boil because the lid's been left off.
Therein lies one of the many problems with site rankings, and with blogs in general: they sometimes get left as the flotsam and jetsam of the Internet ocean. So this leads to other debates: even if a blog is dead, shouldn't the content still be indexed? Of course it should; but ranking for something like a blog that depends on updated content but isn't being updated should be part of the Google algorithm.