Enrollments a 6% decrease in enrollments may be statistically significant, but may not reflect decreased desirability of a US graduate education. This can't be evaluated without also looking at the number of offers made. There are reasons why the numbers of offers may have decreased. Many US institutions have had budget crunches in recent years, which means that a larger fraction of new grad students are going to be supported as TAs. With tuition and fees rising at the same time, we need to be even more careful about taking international students who can teach US undergrads.
My instincts and anecdotal evidence suggest that post 9/11 security issues create problems for recruiting outstanding international students to the graduate programs in the US. Visa denials to new students, horror stories of students being trapped in China in the middle of their graduate studies (we had several cases of this last year) after visiting families or going to conferences, and general delays and unpredictability of whether or not admission means being able to come here can't be helpful. The competition is real, as are the negative effects on our competitiveness of going overboard on security screening for student visas. But this NYT story doesn't provide the right kind of data to support that storyline.