So yeah, not because it wants to be charitable, rather because of existing and possible future regulations. And there are DOT regulations defining significant schedule change and requirement to refund. It mentions connection cities (though only in the context of disabilities) and # of connections. While it's not as strict, it does not lend credence to the argument that airline only needs to deliver A-C with free rein on the routing. You were the one asking whether a court will recognize routing as part of what people bought, and the data clearly indicates that airlines don't want to get that tested out in courts, so they are offering the right to refund proactively.

I do not see anywhere that says no compensation for denied boarding if no delay. While the writing is not good that it only mentions half compensation if delay of 2,3,4 hours, the reading by the letters (though a little unreasonable) will say full compensation if denied boarding with no delay since the footnotes don't apply.

If you still don't agree, here is what United says. "If your flight is cancelled or delayed by 3 or more hours or you are involuntarily denied boarding, you are entitled to receive €600 in compensation from us. If, however, we offer you re-routing on an alternative flight that will arrive within four hours of the arrival time of the flight on which you were originally booked, your compensation can be reduced to €300." So UA agrees that one is entitled to compensation if denied boarding, regardless of the delay. So I'm right and you are wrong. You can not take off someone LHR-EWR-AVL and put on LHR-IAD-AVL involuntarily without compensation.

Well the rule says they need to ask for volunteers first which most time airline will pay enough money to avoid getting into the IDB stage, and even when start IDB, they need to follow a pre defined list which you may not be at the top of the list. (And if you are really at the top of the IDB list, you can just volunteer.) They can't just notice oh, this guy is going to C and let's put him on A-C directly so that we can save the money of asking for a volunteer. That's a clear violation of DOT rules.

So the point stands that airline can not under the name of "we are only transporting you A-C" and force you off a scheduled A-B flight (assuming no aircraft downsizing) without compensating you for all practical situations.

I did not deny it's nice, but I don't have false illusions. I know the cold fact is because of the regulation and threat of compensation. Anyway, I don't think this is a critical point to debate. We can agree to disagree whether it's due to contract or regulation.