Ok, so I live in this world.
The ones with wives of a similar age to themselves usually met them through work, with the wife being of a similar intellect, education and in a similar career at the start. The husband's career has taken off much later, and usually at the expense of the wife's, as she has had make all the compromises when it comes to family life.
The one's with a much younger wife are usually on their second or third marriage/relationship to someone they met at work, who was in a much lower tier job. Quite often someone from admin, or HR. Pretty much all start out as an affair (in fact quite often the wealthy man you see out with the much younger woman isn't with his wife. She's at home, oblivious). Some are very sweet, pretty women, with possibly low self esteem who are very subordinate to their DHs. Some are quite cut throat women who went after what they wanted offering a lot of sex and glamour. I guess either route works 
However, all that glitters isn't gold. Successful wealthy men aren't (usually) just born like that. They are focused, driven, and often obsessive. It can be very lonely is such a marriage, stuck at home with the dcs while they spend every minute of their time working, networking, or burning off steam doing a hobby. Such men nearly always have a hobby.
Oh, and the other thing, wealthy men are often very tight when it comes to spending money (that's how they stay wealthy). So you might live in mansion, but after you've spent years of your life cleaning it (because DH doesn't see why he should pay for a cleaner when he has a wife) you'd probably quite happily trade for a nice 4 bed.
Disclaimer: 1: I have no idea about those who have inherited wealth or got rich quick very young through football etc, the ones I know are highly educated and self made.