So the 7th buttons is the same as one of the six buttons? There is no game that uses all seven buttons for action in the game?
Sometimes the 7th is the same as one of the other 6, but not necessarily. It is really just a matter of whether you wish to assign it its own function or not.
No, unless you are playing conole games in your cab, then there is no game that will be using 7 buttons.
The 7th button, as already mentioned, is just a combination of 2 layouts. Neo-Geo had 4 buttons in a sort of line while many fighting games had the Street Fighter layout of 3 over 3. 7 buttons just makes it easier to play both types of games with their standard layout.