I believe the GM best describes this with his quote
http://forums.worldofwarcraft.com/th...98741&sid=1#13
The lever can be attached to as many levers as you want it to be as long as the result is 1 action. As long as you have to continue to press the button to get more actions to take place it doesn't matter how many levers its actually attached too.
So my 1 key can correspond to any number of keys as long as I need to press it each time to initiate something. This is also similiar to /click ingame as well. You can make a macro to /click as many buttons on your UI as you want. You can set it up to click all the spells in your spellbook and it will only invoke 1 action on the GCD. Things off the GCD don't apply as they share different rules.
So 1 key =/= 1 key per blizzard. It's more along the lines of 1key=1action.
Edit: doh. I really take too long to type. Everything I said pretty much was already said.. lol.