In a sense, yes, telling the phrase is completing the quest for them. But think about it in roleplay terms. If you had a Holy Script of Laanx and someone came up to you and said that they needed "the scroll of Laanx", you'd know what they meant, right? Finding exactly the right words to tell the NPC isn't a very good basis for a challenge. A real spoiler would be something like telling someone where Nyshyn is or who has Falka (which is why I'm not saying it here!). But if the person knows who to tell something and just can't find the right exact words, I don't think that counts as a spoiler.
It seems just like it's an attempt to place the blame on the player for not having figured it out yet, rather than on the programmers for not putting in enough synonyms.
(Of course I do realize that posting all the phrases on the forums where everyone can read them might be pretty bad. That's probably the main reason it's only allowed ingame.)
