That's simply not true. Compared to any other country people in the US give far more.
"Gaudiani said Americans give twice as much as the next most charitable country, according to a November 2006 comparison done by the Charities Aid Foundation. In philanthropic giving as a percentage of gross domestic product, the U.S. ranked first at 1.7 percent. No. 2 Britain gave 0.73 percent, while France, with a 0.14 percent rate, trailed such countries as South Africa, Singapore, Turkey and Germany."
http://www.msnbc.msn.com/id/19409188/
Last I heard, your average US charity has less than 30% of its budget met by donations.