Are't their ad rates determined by traffic? Doesn't increased SPAM traffic make the ads more profitable? The SPAMMERs have to go to a page to post their junk and then return to bump it. The more spam, the more revenue they make, don't they?
Yahoo seems to have stopped dedicating resources to cleaning it off the boards. They give you the REPORT Button to make you feel better but it is not hooked to anything.
Anything they do to stiffle spammers makes real users lives more difficult.