3-letter domain mystery (3.Viewing)

Can someone please explain the mystery of 3-letter domains? I see these consistently bidding relatively high in auctions. Not only there is a large number of potential 3-letter variations, isn't it a complete gamble whether some organization at some point in the future will really really want that particular set of 3-letters as a domain?

I don't think it's that big a mystery, three letter acronyms are so commonly used in business, and some have potential use by multiple companies. Easy to remember, short, liquid, good for emails, a bit of a lottery ticket but also easy to move for at least some cash value. More affordable than a 2-letter. And for all of this I'm talking about .com's especially.

Larger sales pool. I’d imagine there are hundreds of businesses per acronym. AMD, IBM, MSN, DHL, MSI, AOL, and PNC are just a few I thought of in a few seconds.