That's some nice advertising you've got there... It'd be a shame if someone decided to block it...
But seriously, okay... you pay off ABP. A large group of users migrate to another ad-block tool... that tool's creator demands protection money... and so on. That, to me, is why it sounds so scummy -- because ABP can only promise not to block for it's own user-base. It's literally, "hey, give us a cut of your ad-revenue or we'll give a free app to people to prevent you from serving ads."
Does this policy undermine their "acceptable ads" option? i.e. ads are now acceptable if they meet a certain technical criteria or the provider has paid protection money?