It's not so much "money people" as it is utility - someone who can provide you with a $1mm or $10mm business opportunity wears the same quality suit as someone who can provide you with a $100mm or $1B business opportunity. It's a practical method of signaling status within a group where everyone is wealthy.

Humans as well as many other mammals become anxious in groups where their position in the social status hierarchy is unclear. It's a tool for signaling information to strangers, same as a wedding ring.