Beagle,
"My view is that if the WiFi access point owner doesn't restrict access to listed wireless clients (such as by MAC address), then that is tantamount to inviting open access."
That's a bit like saying that if you don't lock the door to your house then it's OK for anyone to go in!
My understanding is that you can be prosecuted for a clear abuse of someone else's WIFI network. Clear abuse would be, for example, where you had no WAP of your own and were deliberately and knowingly using their connection without their knowledge or consent.
The fact that they have left it open may be foolish of them, but it does not constitute an invitation to all and sundry to use it.
Coconutty -
"If the wireless connection was "on" then presumably it wasn't costing the owner anything extra
to have someone connected wirelessly to their ISP - "
So if someone uses up another person's monthly download quota that's OK then?
And if a network is used by a miscreant for nefarious purposes - uploading, downloading or attacking - that's OK too?
Yes, anyone who leaves their network open is a fool, but that doesn't exonerate the wrongdoer.
"No, your honour, I didn't break and enter I just entered and helped myself". "Oh, that's OK then, case dismissed!"