This really does make you think, WHY? Why would a service allegedly moving billions worth in proceeds need to advertise here, and so aggressively even, especially when their customer base seems to be set in stone from day one?
The forum is the ideal place to promote such services, and the target audience is not the individuals inside the forum, but those who read the comments in it. For example, I read comments in many forums without having an account in that forum. This audience will add new Bitcoins to the mixer, and managing the mixers does not require a lot of expenses. In addition to network and hosting fees, mixers do not cost anything.