[Executor]

Diplomacy is an ability to gain strategic advantage and find solutions, so if someone makes a NAP so he can more easily attack it's still a diplomatic move to me, and a good one.

I believe both types of NAPs stated above by Calahan are the same, and should not require "maintainance", however a NAP is basically a show/sign of trust between two nations/players, and it is specifically up to them if they are to find them binding or not, and of course the "house rules", which are rarely stated, and never state that NAP are binding which would be ridiculous IMO.
But still, a player who belies that a NAP in any case scenario is enough of a protection has still quite a lot to learn, and should experience some backstabbing as a lesson.

I don't think that diplomacy is meaningless in Machiavellian games as Baalz states, however it is probably reduced to a lower level and players should be aware of what type of game they are entering and not ***** about it if they get screwed over.

But again, Machiavellian game or not is the same to me, nothing prevents anyone from breaking any form of pact, agreement in any game as all is fare in love and war, and as I said, it would be stupid to assume that pacts cannot be broken, any pact.