Couldn't agree more with your comments about FIDS WHBM. When flying loco I ignore any 'boarding' and 'closing' messages. Instead, I aim to be at the gate around 15 minutes before departure time (regardless of what is displayed on the screens). Usually there is still a significant queue. Often, boarding has not even commenced. In my experience, what is displayed on the flight information screen bears little relation to the actual status of the flight.
Some airlines are just as guilty. Ryanair advises passengers that the gate closes 30 minutes before departure. They also operate on 30 minute turnarounds. Therefore, in normal operations the outbound flight will not have begun disembarking passengers at the time they say the gate closes for inbound passengers. The worst offender however has to be Air Asia, whos flights frequently go straight from 'wait in lounge' to 'final call' in one swift step!