CPMaverick

Yes I hold an Australian visa, in fact I've held many types.

You completely misunderstand the wording in the link that you provided.

"If your Australian visa expires while you are still in Australia, you will become an unlawful non-citizen."

This is expiry, for all the Australian visas I've held and including the ETA, is based on a fixed timeframe after entering the country (90 days, 6 months, etc). Exactly as I stated. It is NOT based on an expiry date listed on the visa itself. That date is only for entry. Once you enter that is irrelevant.

I once entered Australia 1 day before my visa entry expiration date (the only expiration date on a visa) and stayed for 4 months before I renewed it.

Is it the same for all Australian visas? I'm not sure. But all the types I've used in the past.

The UK is also the same IME. Not sure about EU.

I don't want to get in an argument as all that is relevant to a single person is the terms of their visa. All I know is my experience is that this is typical.