Awesome post, agree with most of it. I do think though that even if marriage wasn't a legally binding contract you'd still get idiots that are obsessed with this tabloid gossip. Sadly, there's a very genuine public appetite for this information. See the success of Celebrity Big Brother and Heat magazine. If somebody is a successful director or actor then they apparently owe it to the public to give up all their privacy and be judged.
All these people obsessing over celebrity break-ups would react very differently if one of their friends in real life cheated on their spouse.
Of course they would. The double standard between celebrities and "real life" people is sickening. There's an entire parasitic culture of people who take pictures of famous people doing anything and everything from leaving out the house, walking the dog, getting some ice cream, etc. If these people did the same thing to any regular person doing the identical things, people would be weirded out and disturbed, but think about it; the photographer isn't doing anything differently, the people being photographed aren't doing anything differently. The only thing that's different is the profession of the one being harassed.
I think it's because we as a culture still can't get past the divide between fiction and reality. Now, that may sound a little extreme, but moving pictures are only a little over a century old. When Rudolph Valentino died, women committed suicide because they SAW him up on that big screen and felt like they knew him, loved him. We really haven't moved very far past that. People still watch actors and musicians emote and bare their heart out on moving pictures and we feel like we know them. In some ways, it's the worst of both worlds because the close-ups of their face as they cry about their (fictional) mother dying convinces people that they have a personal, special relationship into the life of this person as if it was their friend, but the detached, intangibility aspect of being only on a screen gives them a God-like reverence. This toxic combination leads to people having incredibly unrealistic and insane expectations for people who just, uh, are doing a job and makes us want to know everything they do in their private life and makes us want to hate them when it turns out they're flawed people like the rest of us who make mistakes.
For a great song on this phenomenon, see "Turn It on Again" by Genesis on the album, Duke, now available on vinyl and 8-Track.