david viewing
While nobody who knows for sure won't be posting it here, it is now pretty widely believed that if there was a major threat to the West from (presumably GPS guided) long range missiles, the Americans would not switch off the whole system; they would selectively jam it over certain areas, and they (and very few others) have the technology to do this in such a way that commercial-grade GPS receivers (even those with RAIM) would not report a problem.
I suppose the purpose of the jamming tests is to test some system which would come into operation in such circumstances.
I don't think anybody cares about GA use of GPS; most people use GPS anyway whatever the anti-GPS old-timers think of it.