"Jose" wrote in message
. ..

I would assume (and I know the etymology) that VORs fail 1000 square miles
at a time, and GPS fails 3,000,000 square miles at a time. Or, more to
the point, there is more systemic redundancy in the VOR system.


The question was, "So why is it presumed that the VOR system cannot fail?",
not, "So why is it presumed that a VOR cannot fail?" The loss of a GPS
satellite would not render the GPS system unusable.