Sometimes they're put there by the hosting provider. The blog author doesn't get the money, it all goes towards hosting costs. Which are, you know, real. Running a blog costs continuous money even if you don't have many visitors because of constant crawling, spam attacks, the need to have a machine online 24/7 etc.
It seems a bit wild if those two could make any difference in costs. I mean, if you have one visit a month and pay per megabyte then sure, Google would maybe show up in stats, but otherwise?
It's not uncommon for lightly trafficked sites to have 90% or more of their resources taken up by bots of various kinds. Remember Google isn't the only search engine and there are many crawlers that aren't search engines at all.
