They have horns for roping work, and bucking rolls.
Big misconception - You will never see a stock saddle with a horn in Australia. It has been added to appeal to the US market and most wouldn't stand up to roping as they are cheap and not the best quality.
I live in Australia, own Australian Stock Horses, and ride in an Australian Stock Saddle.
To be honest, most stock saddles in the US are nothing like the ones we use here. They are generally very bad quality, don't tend to fit very well, and sit you about two inches up off your horses back.
Good quality stock saddles here retail from $4,000 to $8,000 new. Most makers have waiting lists that can be years long. So you can imagine that anything less than around $2,000, new, and in another country where things are normally more epxensive, really doesn't compare.
I got my saddle custom made for me and my horse by a saddler I know and trust and who is very cheap for what he makes. It cost me $4,000.
This is my saddle. You can see how close contact it is, the knee rolls are much more refined and placed more ergonomically than the saddles above. I had mine made with a lower cantle for mounted games.
In Australia, stock saddles are mostly used for farm work, Campdrafting, ASH Shows, and trail riding. Not so much endurance as they are quite heavy.
I see 'Australian' (I don't actually call it that, it is just a different discipline to me, I still do english events in my stock saddle) as closer to english than western. I am talking about ASH shows here. We ride with contact, in a frame closer to a dressage horse than a reiner. We trot and canter, not jog and lope. We are asked for extended trot in a hack workout. But we do also gallop, do stops, back ups, roll backs, and huanch turns.
This is me and my ASH at the recent National Youth ASH Show in the sporting (Gameing) events: