Exactly – this is both easier to implement and has the advantage of not incentivizing people to use something like a VPN to get more bandwidth at the expense of everyone else.
I find it unlikely that Linux, FreeBSD have gotten less efficient since then and the hardware has made enormous improvements, far in advance of the common uplink speed.
ISPs have it especially easy, because they can be assured of being able to distinguish traffic from a given user (hardware control of the medium). It's a bit harder in wireless scenarios, since the client can spoof multiple different IDs, but it's hard for them to keep open a TCP connection under those conditions.