AFAIK Australians can still visit the UK for up to 6 months without a visa.
Yep, as long as they're satisfied that you're doing it for tourism. Be aware that UK immigration officers will often refuse entry if they think you're doing it simply to gain extra time in the Schengen zone.
Yes, it means they were lucky. Remeber - someone checking your passport in the Foreigners Office can easily alert the Straz Graniczna to an overstayer - and as you have to have a legal address, bang.
It's simply not worth trying to get round it - you won't succeed. Even if you do, then you can easily be found out at a later date if the stamps in the passport don't add up.