Giving
"Studies have shown that the richer we are, the smaller the percentage­
of our income we give to the church and its mission. The poorest fifth
of the church give 3.4 percent of their income to the church and the richest fifth give 1.6 percent."
- John Piper

Any thoughts on why this is?

The Minneapolis Star Tribune carried an article on Friday, May 3, 1991, from which these data are taken.