Isn't that a good thing? I mean, if the ISP can't actually satisfy the demands of every user at a given level of service, then why is it allowed to advertise that level of service at all? Its a bit like a sports stadium saying, "Yeah, we can seat 50,000 people, provided they don't all want to see the same venue."
It's called oversubscription and it's a very common practise. Statistically, not all of the ISP's customers are going to use all of their quota every month, so why should the ISP provide enough bandwidth to allow them to? That just means they're spending far more on infrastructure than is really necessary to service their customers' actual requirements.
Also, why should the quota be tied to the speed? When I want to download a movie, I want to download it as quickly as possible, but that doesn't mean I want to max out my bandwidth continually.
Regulating that ISPs never have congestion regardless of customer demand might be a good idea; I don't know. But if it is a good idea we need some way to phase it in so that customers understand what's going on. We don't want better service to look like worse service.
