Chris, I see where you're coming from, and I'd have to say I'm thinking along similar lines.
However:
A grey area? I'm thinking an elephant on a battleship on a very foggy day, here.
Having checked my standard contract, I guarantee to provide " Disco Unit and DJ". Hard to dispute that, I feel.
Although that's true, I don't suspect it sidesteps the question, " are we providing a service comparable to what was ordered/promised"? The answer is probably" no", but as Chris ( and many others, I'll warrant ) is doing, we are striving to provide the best service we can under new constraints.
Is that acceptable? I reckon every case is not only unique, but also needs to be agreed amicably by both sides, in whatever way suits both sides best. I still foresee many " frank exchanges of views".