At the end google adsense isn't the best choice for this forum, it seems the ads slots (now) it is profitable/useful for all the community. As everyone of you told : the security is the most important thing in this forum.
Its not only that, its about anonimity also, atleast from my point of view. With google adsence they would have to deal with taxes, which is not the case with bitcoin payments.
I think they know whats best for them, whatever that reason may be.
cheers