Yeah... I get those as well.
I think they're from mildly retarded 'SEO gurus' that people hire to do SEO for them. e.g. Hire me. I'll spam people and get links for you.
I think the idea is that you scrape information from WHOIS, then spam out and count on the trillions of inexperienced people out there to take advantage of your wonderful offer for a link back, because they heard that links are good.
It probably works to some degree.
Hmmm... maybe I should start a link-back farm on one of my domains that I'm not using...
Very, very, very NSFW domain name
(But I do own that domain...)