I know that for all but two NSW hospitals breech babes are born via c/s. It is another fear-factor thing. The two hospitals that will allow vaginal breech births are for frank breech only (i.e. bum first), footling breech births are still c/s'ed I believe. I don't know what the situation is in QLD, but perhaps you can do some research - there may well be an OB who is supportive of your desire to birth your baby vaginally if s/he is breech and that might be the way to go. (You also may well have more luck in finding support because this baby isn't your first.)
I think it is probably just one of those hospital policies that can't be explained adequately (aside from fear of litigation).
Of course having said all that, as you know, there is still plenty of time for bubby to turn yet. Have a look at the spinning babies website - it should give you some handy tips.