What some of them actually are: lures to marketing or software sites to sell you on whatever service or tool they're hocking. I've seen this so many times now with listings for marketing jobs, and the companies publish a BUNCH of them under different job titles. If you get tricked into applying, you end up sending these companies all of your info: full name, address, email, phone number and work history, which they can leverage to sell you their product. It ought to be illegal.
And don't get me started on the job listings that magically reappear month after month even when they say you're qualified for the role and will keep your info on file for future openings. >_>