In reply to stp:
I think it's an interesting question and you've put it well, so thanks for posting.
Statistically you're probably right and despite what some others might think, this is not irrelevant, as the growing mass affects the greater body of which it is part. This can happen for economic reasons, or just a shifting cultural sense of what is 'normal' or 'appropriate' or 'acceptable'.
Many (most?) gyms require some basic instruction or check or test of belaying skills in order to be allowed to climb at the gym and most involved signing a waiver - no matter how useless that may be, legally.
So, what if the relevant government department, in cahoots with the BMC (seeking validation for climbing to become Olympic etc) decided that all climbers needed to satisfy some minimum skill requirement to climb outdoors - after all, it's been common practice for indoor climbing for years now, it's what most people do, and accept, so it must be OK. Right? So you need to pass a belaying test (booked and paid at your local wall) and you need to sign a waiver (online, small admin fee) or you are technically behaving illegally on Crown land, you will not be covered by an public liability nor will the BMC insure you, or any insurer for that matter. You're clearly unqualified.
Similar things are happening in mountaineering. The stats of climber-numbers for the Nepal Himalaya are pretty gobsmacking to middle-aged fogies like me - huge numbers on Island Peak, Mera Peak, Everest, Manaslu and Ama Dablam then an enormous gap, flitting over Lobuche East, Chulus and other trekking peaks, then a few odd 'expedition' peaks here and there which traditionally and culturally (in climbing terms) made up the meat of expedition mountaineering, or so it seemed. That traditional expedition (maybe 'exploratory') mountaineering is now very much the minority, a statistical outlier. This is starting to influence the bureaucracy there - talks of mandatory guides on 6-7000m peaks for all - and is already seeping into insurance policies. The centre has shifted.
I'm in Australia, not the UK, but I feel it's becoming the same here. Outdoor climbing, particularly what is now amusingly called 'trad' is actually still pretty much a fringe activity, with a lot of concentrated sport climbing and a few busy gyms. Several times in the last year I've turned up with a mate at a classic 'trad' crag on a sunny weekend and we've been the only people there. Of course plenty of people still climb trad, and plenty more now climb quite hard, compared to 20 years ago, but the progression has not been linear - it's concentrated, narrow and patchy. The smoother, greater, growth has been elsewhere - ring bolted sport crags, and gyms.
I helped some friends build the first real climbing wall here in Sydney, Australia in January 1993 and the upsurge in numbers over the next couple of years was incredible - which I saw, and still generally see, as a good thing, as it got more women and more kids into climbing and created for many a pathway that did not previously exist. While I don't doubt it led to people sport climbing harder at outdoor cliffs, it also pretty soon it translated into 'problems' at crags with inexperienced, but confident, people doing silly things and occasionally getting hurt - but hardly in major numbers.
While that might still be a bit of an issue, I think a wider issue is how the statistical change will influence the traditional centre, hopefully not for the worse.