Okay, here's an interesting thought...
Names convey power!
My name is Rose Angmar, although I think I'm much better known as Skylark.
Senrathis Valore, at your service.
you can call me firehart
You may call me Niomah. It is the name I am most often called
I think it is in the book (and possibly the film) Erragon where the quote is made: "To name a thing is to gain power over a thing". This is surprisingly true in reality.
If you are in a crowded room and you hear your name called, what do you do? You stop what you are doing and look to see who called you! That is the exercise of power over you by one who knows and uses your name.
If you give me your IM login name I can then use it to contact you when I want. If you give me your street address and telephone number I have even more power over you!
Where magic is concerned, to insert someone's true name in a spell is to ensure that spell is correctly targeted.
Our druid and magic user may feel they have nothing to fear from giving out their names. Hwever "Atmos" is most likely a nick-name or a first part of a longer name. The same probably applies to Leithanien. Elves rarely have a name consisting of a single word and their common name would be the part with the least power. As for Rose... I'm guessing that she's a cocky human who doesn't have much dealing with magic and actually wants her name spread about.
Rings character actually gives us a pseudonym and mine says it is the name she is most often called!