Their position is: one press on the keyboard = one key sent to each client. They don't say it has to be the same key, and in fact, I saw a conversation with a gm that asked specifically this question and they said it was fine as long as there was a single event per client for each external event (key press, mouse button, etc). Sorry, I can't find it now, so take it with a grain of salt.

I used to fret over this quite a bit until I realized something. You can do the same thing without keymapping in software. I can bind each key to a different action on each client, so that each client does a different thing. We do it all the time with things like our spread-out macros. We also make round-robin (in-game) macros to allow us to round-robin things like frost nova, or thunderstorm. We are, in effect, making each client do a different thing with the same keystroke. The software just makes this a little easier.