What's the difference?

A couple of weeks before we discussed Gov. Spitzer in class and we mulled over the ethics, moral and ethical, of the man in engaging the 'services' of the girl. Although it chanced my mind at that time I was hesitant to ask the question, when everyone seemed to be discussing the degree of un-ethicality (if that's a word!).
But i happened to come across a blog that reflected my thought, so i now feel encouraged to raise this question. What is the difference between paying for these 'services' and an adult film actor being paid for her 'acting'?
If anyone is thinking 'what kind of a question is this', please read on. I agree that Mr. Spitzer's character as a husband is questionable. He could also probably be charged with money laundering. He could also be charged with seeking the services of a prostitute, if it was just as illegal to pay or receive money for 'services' on camera.
As it turns out, the adult film industry is covered under the free speech act, which includes visual content! one of the exceptions to this act are obscenity the definition of which remains ambiguous, at least to me. So logically I am led to believe that if Mr. Spitzer performed the act on camera he would be in legal bounds (not moral).
So the ethical question here is the interpretation of the law. Is the law being interpreted differently by the authorities to benefit the adult film industry?