You may be overlooking some data in your server logs. It does look like "referrer spam" as Jill noted above; typically, those fetches are accompanied by referral data that points to another site.
They are using a program that pretends to be a user clicking on bad URLs as if they were clicking on broken links on other sites. They are hoping you will either link to or visit those sites (I would not do that -- this is sometimes used to spread malware).
If you can check the IP addresses that are fetching the bad URLs you may see some similarities (maybe they are all the same). You could try to block them to prevent the referrer spam from happening again (although if it's someone tied in to the black hat community, those guys swap proxy server addresses all the time -- it's not worth trying to police).
Sorry if that's all confusing. I don't really have time to be both clear and concise.
Edited by Michael Martinez, 26 April 2013 - 12:00 AM.