Huh? You most definitely can "cash out". However, it's extremely limited in how you can do it. You can only cash out money that you earned from auctions, and only if you flagged that to happen at the time you made the auction.
(I'm a Blizzard MVP, so I keep track of these things...)
Derp -- pardon my FUD, was going off second post.
Relevant post from OP article:
Any amount you add to your Battle.net Balance, either through an approved payment method or by adding Diablo III auction house earnings to your Battle.net Balance, will not be refundable (except as otherwise provided by law), and you are not able to convert that Balance into cash. Battle.net Balance can only be used to buy designated Blizzard Entertainment products and services or to acquire items from Diablo III's currency-based auction house. In certain regions, Diablo III players may choose to receive cash, rather than add to their Battle.net Balance, from the sale of an item from the currency-based auction house. Those players will be able to do so via PayPal for an additional fee.
ETA: Actually... I'm still not sure how this complies with US legal tender laws. I still don't see how Blizz can tell players they have USD when they can't redeem the USD. You couldn't, for instance, go to Best Buy and use the USD in your Blizzard account to purchase a toaster, though USD is supposed to be payable for all debts. Not exactly an important issue - I'd guess Blizzard has... you know... people who know what they're talking about who've figured this is legal.