So essentially, if I use the WiFi once at a Westfield shopping...

So essentially, if I use the WiFi once at a Westfield shopping centre, it automatically registers me at any other Westfield shopping centre.

Apple / Android randomising the MAC address would be a massive risk, for reasons outlined above (thanks melenova). From my understanding, Apple have expressed interest in doing this, but it is quite complicated to do and has, to date, failed to work.  Interesting read here http://www.*.com.au/ios-8-mac-randomization-wifi-iphone-doesnt-work-2014-10

It will be an interesting quarterly to read, thats for sure