I've been to AU several times. UK and USA twice. In all cases I've travelled without telling my itinerary. Generally their border control people will only want to see edvidence of onward travel out of their country and/or back to home country and nothing more. I usually just present my ticket for the relevant mode of transport departing their country. Standard practice in most country I've travelled to. YMMV.
They do not check but they ask for it. You got off like most as they did not have a reason to ask further, however when you travel a lot to any of those, you still might get unlucky-ish. I for one got asked for detailed itenary and names of friends I will visit (because I was visiting friends) at the US and CA borders. And at the Thai border for that matter. But then again I travel a lot; when I go for business (once or twice a month) to UK (very strict even though I am a regular and from the EU) & China (where I never had any issues or questions asked), I often add on a trip somewhere else just for fun. The US is mostly quite easy, UK the hardest of all (very annoying).
> In all cases I've travelled without telling my itinerary.
You will have produced at the very least one address you'd be staying for the first night in the country you just landed on. You might have been asked further plans at border control, especially if you are not white.
China recently began asking for an initial hotel booking or invitation letter if staying outside of a commercial hotel for the first night only. Previously and otherwise, no evidence is required.
