Am I allowed to say that 10% turnout of clubs is nigh on unheard of in the UK these days. But it was the quote, and remains so, where folk are motivated to do something. Below 5% and you have a problem looming if clubbing is about action.
What the % is in America, I could not say. It must be less simply due to logistics/distance. For Germany, a for instance. 150 Schmitts on the run, 1,500 schmitters in Germany and surrounding hinterland. Sounds about right.