Be aware that a machine built to operate in the USA will NOT work in Australia without some mods and I am not talking about the voltage issue. New pins are 'country coded' and won't work outside the country they were manufactured for.
How do they do it?
Its to do with the Hz rating on the power. AFAIK in Australia we are 50Hz and the USA is 60Hz. Basically if you jumper the transformer (same as late model pins) for 240v (rather than 110v), the CPU senses the difference in Hz and basically displays a 'this machine is not designed for your country (or similar) on the DMD. There are hack boards around to bypass but from the ones I've seen are messy and to be honest not worth the trouble. Then issues around servicing etc. Mike would be in a much better position to explain the nuts n bolts of it, but I've worked on a Spiderman (Black) which came from the UK (50Hz) and there was a dip switch on the CPU for Australia and there were no issues at all.
All seems a bit pointless to me.
You would think it would be cheaper for them just to make one machine that could run all voltages, like the old days.