It seems to be something to do with the US. The official BA allowance has always been 23kg for EH/TS/AF tickets. The IATA standard is 20kg. For travel to or via Nth or Sth America, somehow the yanks seem to have negotiated the PC (Piece) system. I would be keen to find out why... It looks like all that is happening is that airlines are slowly removing this PC system. For example for UA L/H flights to or from USA it used to be 2 bags @32kg now it is 2 @ 23kg. Just seems like BA is following suit...
One system for all carriers would be ideal, that was no one would say things like... "But United lets me have two bags!"
Good luck to all the ground crew out there.. Happy Handling!