I'm A Banana
Potassium-Rich
If what you roleplay fits the alignments and archetypes (and whatever else) that the rules presume, then the rules might be a good roleplaying game for you. If the rules clash with what you are roleplaying, then it is a bad roleplaying game for you. But I certainly don't roleplay Lawful Good because it is in the rules.
I think that if Lawful Good wasn't in the rules, though, you'd see less people playing it.
That's sort of the idea of "role-playing rules" in an RPG. They help you play a role by making playing the role part of the game. Being Lawful Good is now a part of the game, because it is defined as a game element. You get to make an interesting choice about what kind of character you want to be, and this helps people decide how their characters will act going forward. In 3e and 4e it's not always a very significant choice (less so in 4e), but it's still there, helping people figure out how their imaginary character can behave in this imaginary world.
You can look at Lawful Good and go "This isn't like me, but I can see my hero like this, so I'm going to try to play my hero like this." This makes the game better at encouraging roleplaying -- at encouraging you to take up the mentality of another character and play that character, rather than pretend to be yourself.
Some people start with the "I want to act like a stereotypical knight in shining armor!" idea already fully formed and ready to go. Others might need to be lead there with things like Lawful Good (and the Paladin class from pre-4e).
Not that it's a prerequisite, just that, in my mind, it helps make the game between the books better at enabling role-playing. I personally think 4e could use a few dozen more elements like that.
Aaaaaaaaaaaaaaaand now I have to commit seppuku for entering this thread again and taking it off on yet another tangent.
