Fairdeal,
No, the usual reason is simply that the departure is not yet ready.
If it's a question of departure delay, then we usually push them when they are ready and then remote hold them, especially if there's an inbound waiting to park on that stand.
Sometimes yes, but not always, Gonzo. On many occasions everyone is on board, the aircraft doors are closed and the aircraft is ready to leave, and the first officer or the captain is making apologetic announcements.