In other words, Ashley-Madison is a prostitution website, not an adultery website. "Cheating" is just the hook, to communicate to the users that they should expect sex, but not a future spouse. And the website is upfront about charging for it.
I point this out because a lot of people have gone over-the-top on the adultery angle, such as this The Intercept piece. That's rather silly since Ashley-Madison wasn't really about adultery in the first place.