The article misses something I think makes part of it: grad school is a ticket to establishing some level of connection in the US for foreigners, and some use it as a spring board to getting a job in the US. They need this because a graduate degree actually is losing its value given the poor job market for PhDs. The prospects of a job after graduate school are diminishing the closer you get to a PhD; it just makes less sense to go to grad school when you can get good jobs with just a BS in CS for example...unless there is something else to make the ROI better.

Finally, the stats mentioned are merely fractions, not overall numbers. What could merely be happening is the growth is coming from international students, not that less Americans are headed to grad school.