Except if you are ordered by court to go. Plus there are some situations where its either AA or some sort of huge fine or something else equally bad. I have a good friend on mine that was required to go to AA for weed charges rather than pay a fine and have it on his record. This on his record would have meant loosing his job. He is an atheist and resented the higher power thing greatly.
And forgive my ignorance here Alfie but i always got the impression that spiritual was a water-downed idea term for a theist. Water-downed similar to some atheists calling themselves agnostic because it sounds like a less strong/ more open belief.
I bet he resents getting caught more. I'm sure your atheist friend argued real hard with the judge:
Please, please let me pay the fine and lose my job, your honor! I can't go to AA! I might have to hear them talk about a higher power.