Well you see, adbots are easily taken care of as soon as a moderator of one of the sections logs on and has the chance to ban them. It would be a really pain for staff to have to approve all those posts each day you see, it would also be a complete inconvenience for new members. With every 200 new members we get only about 1 or 2 of them would be an adbot. It's just something we need to deal with for the moment really and adding such a clause for new members would be very untidy, a lot of work and not to mention that new members would find it daunting and quite confusing for that matter.
However, we do have a sort of human verification system on sign up, so the ads you see currently could very well be someone doing it as opposed to a bot but I couldn't be 100% sure. Again though, not a great issue to staff as it's easily taken care of but I think we could find a better alternative opposing post moderations for new members.