You'll also find links like this dotted around on those sites and various other ones
<a href="http://refer.adultwork.com/?R=4928492&T=http%3a%2f%2fwww.adultwork.com%2f4928492" target="_blank">Find me on AdultWork.com</a>
When you click one of these, usually a file will drop onto your computer for a period of time. Any purchases you make on the site, the person who owns the website with the link will get a percentage cut of what you spend. known as a referal fee. Just clear your cookies when your finished. Or set your punting browser to never remember history.
More information about these types of links here
External Link/Members OnlyAll big sites do it, Axxxxxx have the biggest affiliate scheme out there and I've made a tonne of cash through it. You'll notice sites where it looks like it's just pulled things directly from AW and you end up on the AW profile, that's known as an affiliate website.
EDIT: looks like this is being held for moderation, perhaps the owner should take advantage of the affiliate scheme that AW offer