I agree Stu. The mind boggles to think how many English folk songs would have been lost for ever had not Irish folk singers kept them alive. As for blues and rhythm and blues music, it is worth pointing out that until British blues bands started touring the US in the sixties, Muddy Waters and BB King were both virtually unknown in their own land. Indeed, their popularity, which had only ever existed in a small market, had already long since waned. They both generously acknowledged this in many interviews. The musicians, who revolutionised pop music in the sixties, could only possibly have done so by mixing US and British influences.
In some ways, with their swagger and attitude, the Stones are the ultimate American band. However, only spiteful middle class English boys could have written "Play With Fire", "Mother's Little Helper" or "Nineteenth Nervous Breakdown" - let alone the casual vulgarity of "Brown Sugar" or "Honky Tonk Women". If you just hear the bass and drums at a distance, the Stones sound distinctly British, yet they are the template for the ultimate American bands like Aerosmith and Guns and Roses et al. The Stones mixed up what they knew and passed it on. That is what happens in a living culture.