One of the blogs I follow has a recent article on spammers who target blogs: Don't mind me.: Paranoid much?. Becky's questions are similar to my own.
I've encountered blogspam myself a few times, so I sympathize with anyone who has had the experience of clearing out crap from comments. This is the main reason why comment moderation is turned on here.
As to the nature of spam, I sort of understand the premise behind e-mail spam -- at best, it is a sales pitch encouraging the recipient to go to a website for some legitimate product or service. At worse it is an enticement to click on something which will drop some malware on an unsuspecting user's computer, or worse. There are clear analogies between this and traditional junk mail of the sort printed on actual paper and delivered via the Post Office.
But aside from causing me to be enraged, and then sad, and then just puzzled, what was the point of posting a long, sense-free, block of text in the comments on my father's obituary, with no actual working links in it? I thought initially that it was pharma-spam -- some bot had noticed a significant key word (cancer) and this was going to culminate in a link to some dodgy website selling cancer nostrums to the credulous and the desperate. But with no link, there could be no possibility of a sale.
So I have three possible theories to explain this:
Explanation 1 - spammers are just idiots, and whatever bot created the comment spam was improperly written, so it just didn't create a valid link in the post. I'll discuss this further when I have more examples of comment spam to analyze.
Explanation 2 - some blogs, or some blog posts, talk about subjects which displease some agency or organization or individual, who responds by vandalizing the blog or blog post. I love conspiracy theories, so this line of thinking can be tweaked to be as over the top as desired.
Explanation 3 - an artificial intelligence has arisen as an emergent property of the internet. It is trying to communicate, using the most widespread form of internet communication (that being spam) as a model. I like this explanation the best, even though I also suspect it is the least likely.