Since all of the companies fingered as cooperating actively with PRISM were American companies, the assumption is that while the NSA may spy on foreign companie

Since all of the companies fingered as cooperating actively with PRISM were American companies, the assumption is that while the NSA may spy on foreign companies those companies are not actively cooperating with the NSA and it is therefore (in theory, I suppose) harder for the NSA to get at their data.