Actually you need more range that that, those are nominal voltages, and though IEC standards are suppose to be within 5% of nominal voltage I've seen em go as low as 90V in parts of Africa and up to 280V in parts of Australia and Asia Minor.
Supposedly the 240/220 50hz countries are all going to move to 230v (I.E. in the middle).
With any luck it will come down to 230v 50Hz or 110v 60Hz and every thing else will go away. Not that its a diffcult problem any more. Most modern electronic gear has a 'switched mode' power supply, and these can be made 'autosensing' quite simply, and they don't care about the frequency of the input. (The first thing a Switched Mode does is convert the AC to DC, so the rest of the supply electronics doesn't even see the AC frequency).
However agreeing on a common connector (and earthing) is another matter. Will never happen