I should have been a bit more clear. I wasn't saying that a recoil spring didn't do ANYTHING, but that it didn't do anything significant as far as increasing lockup. I realize that the extra poundage will do something at some point, and didn't mean to say otherwise.
The main point Tuner hammered on was that it was a slide return spring, and its main function was to return the slide to battery, and keep it in battery during normal usage. You will see this in the gamer's guns when they run too light a spring with a normal or heavy striker spring, and pulling the trigger pulls the gun out of battery.
I think the idea of velocity swings changing with recoil spring is a myth, regardless of the fact that the guy from Buffalo Bore really believes it. So far I have seen two cases where it should have shown itself, and it didn't do so in either case. What would be needed is someone who understood statistics AND internal ballistics to run some tests that would actually show something, rather than some nearly random guy claiming it works that way.