This is an excellent thread idea and I look forward to the more knowledgeable answers out there.
From where I sit on the outside looking in, not being in the industry nor a real competitive shooter, I think we really have 3 groups to thank for the evolution of the "modern handgun technique"
- The first were the pioneers in the 50s and 60s like Cooper, Weaver, and others who had military or law enforcement experience and realized that the old "bullseye" technique was lacking for any serious purposes. Add to that the NRA who came up with the first of the "combat" oriented matches with the PPC that opened the door for IPSC and all the others to follow.
- Second were the mostly civilian "combat action" competitors who in their never ending search for an edge and to shave a few tenths of seconds, threw common practice out the window and embraced the isosceles stance, press out, and other techniques. Unencumbered by department and institutional SOPs and equipment, they weren't afraid to try new techniques as the only thing they had to loose were matches. This proved to be a perfect breeding ground for new ideas to spring up and techniques to come to fruition.
- Lastly were the elite HSLD military and LE units that looked to the civilian competition shooters and training centers like Gun Sight to train their soldiers and then cross pollinated the more poguish units with their new found knowledge. There was no way that the big Army would ever look to the civilian action shooters for advice and the AMU was largely too involved in traditional shooting matches to be developing new styles, but the guys from SFOD-D and other like units were open minded and embraced change. Once the average soldier saw how the "cool kids" were shooting they wanted to do the same. The past 10 years has brought an abundance of real world combat shooting that has given these guys real world feed back which they in turn fed back into the world of training with guys like Kyle Lamb, Paul Howe, and others decimating their wisdom.
As a side note, I will say that while the Euros might have had some influence (at least with the formation of HSLD units), this evolution of combat shooting style could ONLY HAPPEN in a nation with a healthy civilian gun culture. Ironic when you think that the latest techniques an SAS trooper is using, came from a nation who's gun laws the average Brit would find horrific.