What would happen if those ISPs notice increased profit and customer satisfaction (overall) when they are paying less for resources used up by bots? (Assuming they don't have problems with false-positives or find far too many customers being cut off, etc.)

I'm an engineer and I don't know even vaguely how much bandwidth is used at my house. I don't count up the uses I know about, but there are plenty of uses I don't know about, like automatic update checks, game usage or at worst, viruses using my bandwidth for their purposes.

People flocked to flat-rate pricing long ago because they wanted access, but didn't want the surprise bill at the end of the month.

Another question: do laws have to be enacted to verify that the bandwidth meter is accurate, the way gas stations pumps must?