The belief that atheists are more materialistic than theists isn't one that is founded on any evidence, but it is a popular one. A survey done by researchers in the University of Minnesota's department of sociology found that atheists are the most despised and distrusted minority in America. The most popular reasons cited were "moral indiscretions" like criminal behavior, rampant materialism, and cultural elitism. Evidently being theistic and religious prevents such problems, but since when?
Read Article: Myth: Atheists Are Materialistic & Worship Money, Material Goods, Comforts