DMan's Universal Disclaimer: This is a recitation of my thoughts on experiences in my life. It is probably a generalization.
Also, do not call me sexist. Notice I did not once refer to genders except in my one named example.
Phenomenon observed when a marrying couple is obviously very different in financial status and the richer spouse is generally physically unattractive and the poorer one is very attractive. Also there is a high chance that the richer person is significantly older than the other, stretching it to the 60 years gap once in a while (yes I am talking to you Anna Nicole Smith).
While once in a while these couples may actually truly love each other, I believe a large majority of them do not and the marriage can be dissected into very simple components.
Richer person desires younger flesh
Poorer person desires financial security and an easier access to money
Everyone is happy..........
Until the poorer spouse no longer sexually satisfies the rich spouse
While living abroad in developing countries, I have witnessed a deviation to the money objective. That is they marry for citizenship to rich Western countries. Quite sad actually. I hate seeing a very nice-looking girl younger than me or about my age (I'm about to turn 19) holding hands and snuggling with a fat 60 year old foreigner with more money than me. Ewwwww.