They drive hybrid cars, if they drive at all, shop at local stores, if they shop at all and pay off their credit cards every month, if they use them at all.
They may have disposable income, but whatever they make, they live below their means, in a conscious effort to tread lightly on the earth.
http://www.usatoday.com/news/nation/2008-05-04-growing-smaller_N.htm