Dave, VGS flying is very different in nature to club flying. The entire focus is on teaching bloggsy to fly a circuit. You don't usually get aircraft launching and going somewhere else for an hour or more. A hundred sorties or more per day is not uncommon if you're relying on winch launches, even using around 4-5 gliders- in effect, 200 movements a day.
You also have to factor in things like lateral spacing, runway and taxiway edges and all manner of things that can get snagged by cables (for example radars and indeed aircraft- actual events)