Hi Garry,
Pretty much all that's been said so far as regards to Power supplies is correct. Any new laptop on the market nowadays will have a power supply capable of between 110-250V so can be used in many different countries - after all, a laptop is portable! You'll just need plug adaptors to fit into the sockets of whichever countries you visit - look on ebay or places liek Dabs.com or Ebuyer where you can buy individual items or travel kits for not too much outlay.
As for which machine to go for, I know you have your own business, I'd suggest looking at a good business laptop. The MacBook air is a 'nice looking machine' but pretty inadequate as a serious machine (lack of an ethernet port, hello Apple this is the 21st century! single stingy USB port, enclosed battery and battery life isn't so good either)
Have a look through this group test. The Dell 630 winning machine is excellent, and you'd have change in your pocket compared to the MacBook air or Macbook pro if you went for one of those.
I can't find it right now online on that website, but this months magazine, they tested a Macbook air Vs a Lenovo ultraportable laptop - the Lenovo trounced it in all aspects.
Have a look at other review sites as well, it'll help you make a well informed choice. Of course, if you are an Apple fan, I'd say go for the MacBook Pro simply for it's better power under the hood.
Hope this helps
Cheers, DtM! West London & Slough UK!