Bhagwan,
The reason the NSWTAB wouldn't like this type of bet is that rather than take 4 lots of 14.25% from the win pools in question they could only take one cut of say 18 or 20% or whatever they decided to skim. It's the same reason they will never bring a quaddy to NSW.
They like the all-ups because your wins are being slashed by 14.25% each leg. The cumulative effect of this is horrific. No-one should ever bet all-up or parlay on the TAB. It is a gross waste of money and value.