You have made an interesting point. I think for certain personality types, status is a powerful motivator, addictive even. This is not based on any studies I've read, just my interaction with an assortment of people and observing how they revelled in their status and the trappings, or were quite indifferent and were just themselves.
It will vary a lot based on the situation/environment. Cost of living in different areas will be different, then there is the factor of how many people you are supporting off that income and the health condition of each person etc. There is no concrete answer since there are too many variables to consider.
My opinion is that it's total BS. I think you have happy and unhappy people at all wealth/income levels. One thing that I've seen in my life is that many very successful businessmen are completely obsessive about their business and therefore are constantly unhappy or upset about something. Many of these people are perfectionists and very demanding and when others can't live up to their expectations they can't accept that. Many wealthy/successful people that I know are also workaholics, and very frugal with money (at least from a business standpoint). So much so that they are constantly upset that someone is ripping them off. This could potentially skew the results a little, however it's not how much wealth they have that makes them angry. These people would be angry regardless. And in fact, their anger is often times their edge that drives them to succeed in business. A less wealthy person might have that same mentality, but possibly turn to crime or alcohol abuse, rather than channel their energy towards business.
"Everything is wonderful, and nobody is happy." Louis C K "Give it a minute, it has to go to space and back...." The bottomline is, without the cost of living throwing out of dollarvalues is silly. In Vietnam you can live like a king on 20K a year....
Being rich can feed the ego. Some people will think they are happier. But it is just an illusion created by the ego. In reality your day to day emotional experiences wont be any better than someone who earns a comfortable living.
When Buffett felt a bit jaded he went out and bought himself a railway. Can't do that on 60k a year. CHOO CHOO