(I don't know if this was hotfixed, but the NPC still asks for 90.) I went up to the Mogu Rune quest to get the quest, and I only had about 55 Charms, I Accepted the quest, the ? indicator was golden, confused; I clicked the quest, and behold it let me complete it!
I had 5 leftover.
In short, Mogu Runes quest is glitched ( I assume) and only requires 50 Charms, not 90.
View image: Mogu (Shows quest prior to completing, I dont have enough charms on this toon I took the picture on, I didn't think of taking a picture of it at the time ._. )