I make ADR's and keep them. I wait if the restaurant is running late. However, in the event I was told 40 minutes at LTT I might have asked to cancel. Your waits were shorter, but not all are. The op did not ask to go ahead of the pack, she wanted to cancel because the restaurant could not accomodate in a reasonable time. I think that is fair.
If the restaurant wants to charge that cancellation fee it better be able to seat me in a reasonable time frame. I understand ADR's are not true reservations but if Disney wants to treat them as though they are, and j support that, Disney restaurants need to manage their time better. If the restaurant reserved the right to cancel an ADR and charge the fee if I am late they better be willing to either seat me on time within reason or let that fee go. If I do not choose to wait.