[noclip]

If you pay for (say) a DS3 line, there's an implicit assumption that you are not going to be pumping 44.736 Mbit/s through it 24/7.

Whoa, whoa, whoa. This is exactly the assumption commercial customers paying for unmetered links are making, otherwise they wouldn't be paying for unmetered links. Not being oversubscribed is supposed to the entire point. If ISPs' business models depend on them being able to break their promises to customers paying for continuously saturated links that's their problem, but they're still on the hook for what they're being paid to provide.

[ghshephard]

I'm looking forward to chipotle_coyote response on this, but I don't think he's referring to the circuits that commercial customers pay for, but instead the ISP peering circuits - which are usually expected to run at much less utilization.