Hey Art,
this thread will shed some light on it.
Emerald, I took this bit of text from the page that I linked to in the thread above.
Why do people do this? There are two main reasons.
The first is to get you to follow an affiliate link, in the hopes that you just might like what you see on the page you view, and be enticed to follow it. You will often see referral spam for products / sites that are somehow related to your own.
Another reason for log spamming is for the backlink or pagerank factor. If your stats are available on a publicly viewable page (ie. if you go to www.yourdomain.com/stats/ to view your stats without having to enter a username and password) you are a much greater target. Some stats pages have a pagerank value to them, and a backlink to the site can help with the search engine rankings.
Hope this sheds some light on referral spam.
Edited to add: This tactic most likely doesn't work very well now, but a few years back it was probably more effective. IMHO these guys are wasting their time with the fake hits.