iLuvPx,
The main reason that HK has 2 GMC is the useless design of the tower.From the GMS you can't see any of the north runway taxiways.From GMN you can't see the south runway taxiways or the cargo apron.It's a bit difficult looking through a concrete floor.The supervisor used to be non operational,although some did help out.
Also the GMC are responsible for the pushbacks on what the Americans call ''The Ramp'' so it's not the same system.If you have ever seen the pushback chart at HK,then you have to be extremely careful not to get the golden towbar award.
