I have theories about why sleb marriages seem less likely to succeed.
1. Actors. Acting requires emotional intimacy from day one of a new project. Actors therefore tend to be (in my fairly extensive experience) a little trigger happy with the infatuation experience. Meet a new person you click with, even just as friends, and they quickly become your new favourite thing in the world. Also, yes, sometimes snogging.
2. Famous people have people throwing themselves at them. A lot. A friend of mine is a fairly successful stand up whose been a minor "name" for quite a long time. He regularly gets propositioned, and has sometimes advised younger stand ups that "it's not you they want to fuck, it's the microphone.". I bet even Coldplay have groupies. And even if you never give in to temptation, you can't help but be thinking "I could do better".
3. Rich people are surrounded by people whose jobs depend on making the rich people happy. They are treated unusually well. In Hollywood this becomes truly bizarre where anyone expressing any interest in working with you will tell you that you're the best thing ever, send gift baskets, etc. and then you come home to someone who gets irritated when you leave toothpaste on the sink or the loo seat up or whatever. Would guess that if might be very tempting to see your partner's normal irritation with you as being deeply unreasonable. After all, everyone else thinks you're amazing and that nothing is too much trouble to help you.
Anyway, that's my theory.