I own an ISP. This is the second one I've built from the ground up, and it too is profitable. (the first was sold to a Dot Com three years ago.)
DSL subscribers and cable subscribers don't pay for the bandwidth they use. They pay enough so as an aggregate they cover the costs of providing all of them service. If ever we reach a point where more than rougly 12% of them start using the full bandwidth, the whole service becomes a loss-leader.
I'm sorry Paul B, and your signature on your DSL checks in mind, but your $40 does not entitle you to what you're probably using EXCEPT that your current DSL provider is willing to give it to you and take a loss.
Bandwidth at the OC-3 (155Mbps) level is currently $180-$200/Mbps/mo. That means your $40 would buy you 200Kbps and no more.
Bandwidth at the DS-3 (45Mbps) level is currently $220-$250/Mbps/mo. That means your $40 would buy you 160Kbps and no more.
Bandwidth at the DS-1 (1.5Mbps) level is $650-$850, or $433-$566/Mbps/mo. That means your $40 would buy you 100Kbps and no more.
Those are the real numbers your ISP of choice uses to buy bandwidth. They sell it to you at $40/whateverMbps because they figure you won't use it, and they can oversell it, and they'll make their bigger numbers.
If you (all) use it, they can't oversell it, their network becomes oversubscribed, they have to buy more bandwidth, and they lose money.
I suspect Comcast didn't enjoy this story -- it suggests they are looking to get Fresh New Revenue, not "get paid for what people are actually using." The latter would probably have been a fair way to put it that would not strike a discordant note with readers.
Back to the grind.
Mman

for kl