The whole time thing around flying is quirky. I generally agree with OP as I'd prefer to know what time the door closes. I believe the time before departure varies amongst airlines and the time I need to be at the gate would be much more relevant than the scheduled departure.

The one that also gets me is, once in the air, the estimated arrival. Some sources give actual touch-down, some give gate arrival and others seem to just guess at something. 95% of my flights are Hawaii to mainland and I am amazed at the accuracy of the flight time given by the crew on the plane. They know to the minute when touchdown will be 5-6 hours later. I guess they can just compensate for weather/wind changes in the air. By far the biggest problem when arranging for a ride, etc. is getting stuck waiting for a gate. If not for that I know to the minute when I'll be walking out to be picked up.