Dave thanks so much. I guess the important thing is not to mix and match APs, so as long as APs are all one country code you are ok. This is really helpful as the cheapest WW R720 APs I can find are about 50% more expensive than the US ones. Finally I get it!!
For anyone else reading this, even for the UK, Aus, or anywhere else I can think of, the UN00 version should be fine as its the transformer is 110-240V and all you need to change over to another country is a new mains cord, or even just change over the mains plug.
Thanks all!