The answer is quite simple, be honest about the service you provide. It is prohibitively expensive to provide maximum bandwidth 100% of the time to 100% of customers, in fact it's probably impossible.
The US is currently, and very slowly, upgrading it's comms, but atm it still largely relies on 1960s and 1970s tech to push internet into people's homes.
While areas of fiber connections exist, and certainly the backbone of the internet has been upgraded, the majority of users are limited to whatever their local cable or telephone companies can afford to install.
So again, the answer is simple - be honest about what you can and can not provide. Comcast are arseholes. They lie about service, are a monopoly and can get away with it. They do not just throttle back torrents, they throttle back ALL internet service. But they're also not alone. Just about every major cable internet provider in the contiguous 48 states does the same thing.
The thing that gets me is in a state like Alaska, with it's remote locations, huge areas, unfriendly weather and a host of other difficulties has providers that offer a far superior service than most of the "easy" states. The reason for this is the local telecommunications companies have invested heavily in their infrastructure and continue to do so every year. It may be convenient to suggest that providing internet to 1/2 million customers is an easier proposition - but it also means a lot less money. So if they can afford to keep their equipment uptodate, purchase sufficient bandwidth and offer services with no throttling and no limitations on the downloads, why can't the rest?
Personally I think the monopolies in the lower 48 states should be broken up, because it's clear to me that smaller, independent providers can provide a far superior service with more consistent connection speeds.
As for unlimited downloads, this is something you pay for here. You can have the same service as everyone else for the same price as everyone else, or you can pay more and get unlimited uploads/downloads.
But having used both services, and having used torrents to download things like Linux, software updates and maybe the odd movie - I've never been subject to any sort of throttling.