It’s not something that Americans in general explicitly believe, but you can see it in their attitudes and behavior towards the rich and successful. For example, HN (being somewhat weighted towards American cultural norms) collectively believes that people who have made lots of money are especially wise and hard working, and therefore have special insights to offer to the rest of us. True or not, this is a culturally specific belief.
I think this is just a bias. I've not seen much that makes me think Americans think rich people are more virtuous, at all. Certainly not enough to create a stereotype out of, even if I thought stereotypes were a good idea.