The jury is still out on the wi-fi channel issue. What's clear is that channels 1-11 are ok everywhere. For the N800 most of us believed that the hardware is the same everywhere, and getting access to channels 12+13 (and 14 for Asia) was only a question of which country you set your N800 up for. Some still claimed there was a hardware limitation.. and nothing conclusive came out of that before the discussions dried out with some links back to earlier arguments. Anyway, with channels 1-11 working everywhere you're pretty well covered though, whatever the truth is about this.

As for the charger - the N800 came with a full 100-240V range charger everywhere afaik. Don't know about the N810.