The person said that there was a strong correlation...not that some people aren't still materialistic.
Seriously, though, once you hit a certain income, you lose a lot of stress over not being able to afford necessities (as well as some added things that make you and your family more comfortable). Once you go well beyond that line, some people are indeed happier, whereas others might become less happy because they think that they should be happier and are then left feeling unfulfilled.
Also, and I'm only speculating here as I haven't done any research, I'm guessing that most people who make a lot more than that in salary are working very hard and very long hours. Not all of them, but probably most. That doesn't necessarily equate to being happier. Sometimes (as workaholics tend to gravitate to those jobs), but not always. Take me - I'm generally happy to not be doing s**t, and I don't need a lot of money to do that.