People spends thousands (even hundreds of thousands) on a rock (diamond), so I don't see why it should surprise you
Diamond is available on this planet in a finite quantity and will generally only ever go up in value. A few lines of code can always be replaced by... a few more lines of code.
And do you really not understand the problem with this? Markets only work when they are reasonably free. "The Diablo III Market" is quite obviously run by and for Blizzard. It's a scam. If you buy into it you've been scammed. If you don't realize this you're retarded.