OK I'll bite.
Have you ever flown a Vigilant? If you had you'll notice it has a tailwheel and a three position prop, both of which require a PPL to do differences training to use. Most VGS instructors will have been transit qualified having been trained to navigate the RAF way, Dead Rekoning with chart, compass and stopwatch. Who needs nav aids?
How many PPL practice a Forced Landing every time they land? How many PPL would mess their pants if the engine stopped in flight? Vigilant instructors did it for training and for fun, especially if their passenger was a PPL or best of all a helicopter pilot.
I had 1800 hours on Air Cadet motor gliders when I went for a PPL, it was also the first time I had ever used a nosewheel undercarriage, can't see why people think they're better. As for ground school I just sat and passed the exams and then walked away blaming the Air Cadets.
Conversion from Vigilant to Tutor shouldn't be a problem, although I fear the Sliver Winged Master race will make it such.