I think the same type of Pommie regime is responsible for the single deck push in Sydney. Time to reintroduce transportation, the one in-chains type. Back in the other direction. (I'd have to exempt myself though!)
PTC Vic did actually issue a tender for double decks in 1990 and everybody ran around spending much time and money preparing tenders, only to be told later there was no funding. Doh. The very nice Comeng design is in vol 5 of John Dunn's book.
I support Roderick's comments. In Sydney the loading issue/dwell was much-tested and the double decks can very much match single decks like Melbourne's - with the added advantage of higher capacity. They were just stupid about it in Melbourne, but never mind, Sydney is about to become stupider. Intercity rivalry lives on in a race to reach the lowest common denominator first.
A pity - I've always though Melbourne has the framework for the best public transport system in Australia but they seem to keep shooting themselves in the foot. In Sydney, we first destroy the framework, then we shoot ourselves in the foot just to make sure.