I don't think that is it, at least not entirely. I do know some greedy wealthy people, no matter how much they have they always want more. All their wealth might as well be ashes in their mouths.
I also know plenty of poor people who aren't greedy and have little concern for their situation. They chose it, and they are happy with it.
The real truth is that with morality comes a lot of peace and the ability to make farsighted decisions. Often, that leads to more prosperity.
I'm not saying there aren't greedy wealthy people, or that all wealthy people are greedy, just that wealth makes it easy for you to seem nonchalant about money.