A seriously distrubing quote from that site:
"...Examples of benchmarks identified by the group included the following:
-- The proportion of U.S.-citizens in science and engineering (S&E) graduate studies within the U.S. is declining. From 1994 to 2001, graduate S&E enrollment in the U.S. declined by 10 percent for U.S. citizens but increased by 25 percent for foreign-born students. In 2001 approximately 57 percent of all S&E postdoctoral positions at U.S. universities were held by foreign- born scholars...."
and I haven't seen a source yet that talks about what has happened from 2001 to 2004 - I imagine the trend described there has become even more acute as matriculating students choose their course of studies.