Referrer spam, would be one of my guesses -- trying to increase search engine rankings by having more links to their page.
Yah, old enough that I'd figure Google et al know about it and can de-prioritze such links in search engine rankings. Though yah, they might also be trying to get the occasional curious person wondering why a period is linked, whose finger is itchy enough to click blindly without mousing over it to see where it goes.