The trouble with all of this theory, of course, is that it pretty much screws over players who are new to the game/server, who actually want to play the game and not spend their first few weeks just playing the AH. My new druid just hit level 50 on a server where I have no other characters or support structure... atm, I have about 350G on hand, from selling herbs I've had left over from Alchemy and various other goods I've picked up along the way. If I were to actually buy enough glyphs to fill out both of my specs... well, I couldn't do it. I don't have enough gold on hand.
Honestly, though, that people are willing to pay upwards of 90g for glyphs that take less than a stack of some of the lowest level herbs in the game is nothing short of mind-boggling. Even on my level 85, where I have plenty of gold on hand, I would never consider buying a glyph for more than 50g, and I would only buy a glyph for 50g if I absolutely needed that glyph right now and had no alternatives, and it were a glyph that took herbs that actually came from high level zones.
Of course, I also have a hard time figuring out why people are willing to spend more than 2g per herb for things like mageroyal, which is so easy to obtain that it's laughable.... the only thing I can come up with is that people are lazy, and willing to let themselves be gouged as long as they don't have to do as much.