Economies of scale. The price is relatively high due to the low volume of production. These are hobby boards. The only reason you can build a $200 PC right now is because the hardware gets production runs in the millions or more.

Sure, and also maybe the chicken-and-egg problem?
There won't be any scale until there's significant demand, and there won't be any demand while those boards cost so much, that even most ARM enthusiasts would find it difficult to justify the purchase.
It's okay that the performance of those boards would not be stellar, but with them being so overpriced, the result is that the price/performance absolutely BLOWS -- and that's a big problem.

This has 4 times the memory, twice the clock speed and twice the cores of the Pi, of course it isn't going to be less then twice the price. Everything else being equal you might expect nearly 4 times the price (i.e. ~$130)

So, $130 for a bare board with CPU and RAM?
Yeah that would sound great, except when anyone can build a whole PC for $191, http://www.pcmag.com/article2/0,2817,2392163,00.asp
With 2x the RAM and a CPU that rips the ARM on PandaBoard into a thousand of tiny teddy bears in terms of performance.
And a frigging 500 GB HDD (ok, pre-HDD-crisis).

You could say, "yeah but it's not ARM and low-power etc". Okay. There are now Chinese tablets with comparable specs, http://www.aliexpress.com/product-gs/509457480-CPAM-Free-shipping-10-1-superpad-3-android-2-3-tablet-pc-flytouch-3-GPS-512MB-wholesalers.html
that cost $125 shipped. Including stuff like 10" touch screen, camera, internal flash, battery, casing, etc, etc. There's no way a bare board should cost $130. It's just vendors up until now felt just fine with hiking up the price as much as they desire, because those who need it (for development etc) would buy it anyway, or even buy on their company's funds. But hopefully the Raspberry Pi will beat some sense into competitors in this area, and this will move an ARM PC from the ranks of a too-expensive-to-be-practical dream, to reality.

http://www.genesi-usa.com/products/efika
http://trimslice.com/

> Do they have them for $100?

Sure, why not?

Checked eBay lately, you can get yourself a 7" Android tablet for like $65.

NanoNote has many virtues, but being cheap and "accessible" (third world, blah blah blah), is NOT one of them. On the contrary, it is WAY overpriced for what it is. And likewise so, this new wireless addon - 41 Euro, for god's sake, and you were saying something about students and poor children?

You mean something like this one?
http://www.dealextreme.com/p/m001-7-touch-screen-tft-lcd-google-android-1-6-tablet-pc-w-wifi-via-mw8505-300mhz-39169
http://www.dealextreme.com/p/7-touch-screen-tft-lcd-google-android-1-6-tablet-pc-w-wifi-camera-via-wm8505-arm926-42070
Google or see youtube for "Eken m001".

True, but its spanning is better than with LVM. You get what the parent asked, "1 disk dies, I no longer lose everything, the filesystem is easily mounutable and I only lose the files that were on that disk".
And for redundancy, one can use mdadm RAID on the underlying devices.