In reply to johncoxmysteriously:
I think you should dig up that link John! I can imagine admitting that the same *could* be true at 4a, but I can't see that it is generally true...
Around 4a-5a, most moves are between stable positions where you are stood in balance on your feet. Almost all climbers have legs strong enough for climbing (who trains their quads?), so everyone from your 4a climber can rest and recover between moves. This isn't true in the harder grades, where your weight is still on your (relatively weak) fingers. This means moves can blend together. So whilst it is sometimes true at 4a, it is often true at 6a, and almost always true at 6c...
A good example of this is Hubble, in which the crux is not so much the moves themselves, as adjusting your feet and body position between the moves. The dominator example was that the sit-start went undone for some years, yet only adds a single 5b move to the existing, english 7a, problem.
Anyway, the ceiling hit by english tech grades at 6c probably has nothing to do with that, but more to do with a reluctance to stick your neck out in a culture where overgrading and hype are seen as some of the worst sins a climber can commit...