This basically just reaffirms the submitter's point. The PC-in-a-keyboard is not a thin client--it's a full, although lightweight, computer in a keyboard. It's $100. Want to buy an actual thin client? Expect to pay $300-$1000. Throw in a keyboard and monitor, and that ups the price quite a bit.
Also, the argument that thin clients are "specialty" items that drives up production costs doesn't hold up, since one would assume the $99 computer-in-a-keyboard is also a specialty item. It contains, at a minimum, a hard drive and a keyboard, which is already much more than a thin client has (not incl thin client laptops).
So why are thin clients so expensive? I've had the same question for a while now, since I've been looking around for a thin client laptop that's cheaper than a traditional laptop/netbook. So far I haven't succeeded, with most thin client laptops being much more expensive.
My guess is that the marketers hear phrases like "high security," "low energy consumption," "remotely managed," "longer longevity," "virtualization," "cloud computing," etc and think they have features that can drive the price up. The geeks, though, understand that they could build their own "thin client" by just subtracting physical parts from their existing computer and doing a little configuration.