Hey, Dave, I'm not arguing to drop Green & Blacks from the list!! 
Parky, my thinking was:
Friends (back in '77) - camming protection radically changed the nature of routes that could be climbed, first by the elite and then the majority
Sticky rubber: Similar thinking (although maybe i'm less sure....)
Mountain bikes - it's a bike, like a Land rover is a car. Some people went into the mountains on bikes using 'standard' bikes beforehand, but the advent of the mountain bike broadened it out to become a mass participation activity. You didn't meet hoards of cyclists on the mountains back in the 70s and 80s, and you didn't have constructed downhill bike routes on Aonach Mor and Cairngorm (or the summer usage of Alpine downhill ski resorts).
Oh, and climbing walls
- helped to create a generation of climbers who could train and push the boundaries further. Also a ggeneration of climbers who come to climbing as an athletic / physical activity, and an 'urban' one rather than from the 'mountaineering tradition'. Also saw the genesis of competition climbing, which has changed much of the perception of what climbing is about and the focusof bodies like the BMC. (I took part in a major survey a few weeks ago on account of being a BMC member, by Sport England, looking at the 'development' of the sport - it's entire focus was about 'the facilities, the coaching, the competition, your 'performance', disabled access etc. I'm not saying it's all bad but it's a world away from what got me into the outdoors).
Edit: and the Thermarest / inflatable mattress 
: purely a comfort thing here, but I'm speculating that more people camp and backpack as the comfort attainable increases?
As for your "the gps is probably the most important tool" - has it really made that much difference, yet? How many walkers have them? How many use them? They haven't exactly been taken on board yet by bodies like the MLTB etc. in their training (mind, neither have trail shoes, lol!
). I suspect they've had a bigger impact in other areas like marine use than in the outdoors.....