Often when I set up a new customer on my MYOB system, there is address data missing. Quite often the postcode needs to be looked up and I either have to go to the Australia Post website or call the ...
I have worked with ERP systems which are "localised" to suit regional requirements. In fact MYOB has localised versions for New Zealand and Australia in terms of GST requiremnts.
So, in terms of adding address validation, I would consider this another "localised" feature which could be added to the functionality.
As I said in my initiasl post, it is probably not a high priority item but certainly possible.