I am not surprised with this article from Yahoo News. I do not believe that happiness level is set in stones either.
Happiness is whatever you define it to be. Happiness defines by monetary standards usually comes with stress for me. I learned to be contented, living within my means, doing what I love and having people I love around me. Religion plays an important role in dealing with stress, daily pressures and solutions of the heart. I allow myself to rest if things seems to be out of hand because a tires stressful me is of no use for my family.
So, choose to be happy, do what you love to do, always remember Allah and stop sweating the small things!