Anyone out there with a sense of trading?

First of all.... thanks for Cata - made a fortune on the AH ^^

But... however... there are some people out there I actually don't understand when they post things in the AH...

I.e. I go to the AH, search for a specific gem I have crafted. Search result end up empty.
Ok... profitable situation here... simple supply and demand... no supply -> prices go up.
Let's say I put 2 of the gems on the AH at a price of 200G each. Next time I drop by another player has decided to try to sell the same gem. But he puts it on AH for 50G.
My question here is WHY?????

I know that if someone looks for that specific gem they would by his gem and not mine... but they would also have done that if his were there at a price of 199G.

Aren't people doing business at AH looking to profit?

Well, just curious....