They're not the only airline to specifically forbid their use, but with a moving map feature I've no idea why you would need to on VS.
Instead of specifically forbidding the use of GPS devices most airlines will simply not include them in their list of approved devices, and non approved devices are not to be used at any time and thus if GPS units are not on the list then they don't get used. They may be passive but they are still receiving a signal which is where the interference issue may come in to play.
It is the same on BA "Any device that transmits or receives communications but does not have a ‘flight safe’ mode, must be switched off for the duration of the flight" and neither easyJet or BA include GPS devices as an approved device.
It seems Vs is making it crystal clear that they are not allowed. That's my understanding anyway.