Imagine going to an all-you-can-restaurant and having them you (after you've committed to the meal), "Sure, it's all-you-can-eat, but you have to wait 20 minutes after each plate before you can go up and get another."
An ISP, like any other service provider or vendor should be required to deliver what they promise. Simple as that. When they advertise using such words as "unlimited" and "faster than everything else" but then go on to say, "Oh, wait, you're using too much, we didn't mean you could have THAT much," that's fraud. If they are going to regulate bandwidth, this should be stated up front before you sign up. As jdp pointed out, the phone company can't just limit your phone service because you talk too much. Recall that when dial-up ISPs started proliferating, the phone companies did react with panic, laughably worried that people keeping phones lines open for hours on end was going to cause untold problems with the phone system (this reminded me of how the US Post Office whined to the federal government that the new trend of everyone sending Christmas cards was going to be the ruination of the postal service by causing it to come to a grinding halt through sheer overload).
The problem is, although ISPs do usually offer various levels of service to suit different users' needs, they only promote speed, because the average consumer only understands speed. Far fewer customers understand bandwidth, so the marketers usually don't get into it. It's kind of like the way manufacturers of telescopes emphasize magnification power since that's what most people who aren't already avid amateur astronomers can relate to, when in fact such factors as aperture size and focal length are much more critical than magnification power in a telescope.
It's also worth pointing out that a lot of people also don't realize that their upload speeds are a fraction of their available download speed. It stands to reason that this would have an impact on P2P transfers--you're ability to download is only as good as your peers' upload capabilities.