Re: My Little Pony (Original title: The... um, yeah. The bronies thread.)
Wasn't the first time right after she got turned normal after being Nightmare Moon? I imagine she had a pretty good reason not to act like she did this time...
Nightmare Moon IS Luna, at least an aspect of her. It would make sense for Nightmare Moon, then, to speak similarly to Luna, and vice versa. Luna just doesn't go around threatening eternal darkness and what-not.
However, for sake of argument, let's assume Nightmare Moon speaks differently from Luna because, well, yeah, she probably doesn't care for that 'royal' way of speaking. Even then, when NM is defeated and reverts back to Luna, if the 'royal' way of speaking is how Luna normally speaks, even if she uses a more informal tone with Celestia and given the circumstances, there would still be elements of it there.
That's how my mind interprets these things, anyhow. For all I know Luna only speaks like that to the citizens, and when it's just her and her sister she speaks just like everypony else. Perhaps she even makes a lot of 'horn' jokes. IDK.