If I understand you correctly, you're saying that one party may do fairly well in the absence of a prenup, so is actually more likely to breakup rather than less.

That's a good point, and not something I'd thought about. Perhaps as I'm not very wealthy, these questions are so hypothetical that they sound a bit ridiculous to me. If I had a £200 million in the bank I might be more inclined to worry, no matter how in love I was. More money, more problems!