Les-70, I agree with you in principle, but you are fighting the great "We can't do that, we've never done it before !"
About 1960 the GPO got round to fitting proper closed magnetic circuit microphone transformers, to their 'phones in place of "induction coils", which sounds like something left over from the telegraph. The result was a considerable improvement in speech quality and reduction in noise.
Microphone transformers had been available since about 1900 !
In fairness a large system can't be changed overnight, compatibility, spares, training of maintenance people etc takes time, but 60 years ?
Switching off the modem results in a drop in speed (at least on ADSL) since the DLM can't get a response from the modem and so assumes the line is faulty. If a modem could be designed to call up the exchange at switch on, and the exchange then check the line and set the speed, like a computer interrupt or a radio net I don't know, I suspect it could (but the modem would have to wait !) but if it takes a telcom system 60 years to catch up don't hold your breath !
"I am surprised the “green” lobby does not bash BT over this."
In fact the power isn't wasted if it reduces the demand on heating by a similar amount. The effect on modem life may be significant, but there is a counter argument to that, reduction of switch-on surges ( burns out the valves you see !)