Bill,
Yes, I'd tend to agree with you there.
A lot of the larger ducted systems that I've been involved with installing, have needed extra 2-stage heating element banks to supplement the normal heat produced by the compressor.
These banks are nearly always 3 phase units to balance the load over the supply better.
But, like anything, a Ducted Air Con system is only as good as the air temperature sensors that control it and if these aren't installed properly, ie: in the right places, they may as well not be there.
Bjarney,
Over here, the use of 3 phase for domestic A/C is pretty rare, you'd have to be heating a pretty big area to use a Cassette unit in someones lounge.
Having said that, I have wired a unit called a Multi-Head unit made by Mitsubishi and it had 6 indoor units and 1 outdoor unit and all the indoor units communicate with each other and the outdoor unit, it was a wiring nightmare, it was like hooking up a telephone exchange at the outdoor unit!. [Linked Image]