Because it's the price of a textboox.
http://www.geek.com/articles/chips/why-a-25-pc-because-its-t...
http://www.geek.com/articles/chips/why-a-25-pc-because-its-t...
In my experience they start at at least $50. As in, a book that would normally cost about $25 suddenly gets at least $25 slapped onto it the moment publishers realize it's being used as a text book (you can see this quite readily in CS/tech books with equivalent binding). The second publishers realize they have a captive audience they jack the price.
Raspberry Pi is a charity "to promote the study of computer science and related topics, especially at school level" and the device is aimed, in part at least, for use in teaching programming to children.[1]
$25 (roughly £15 at current rates) is a good rough price for a school textbook in the UK. A quick Amazon search shows this.[2]
Bear in mind, too, that the product is aimed in part at developing countries, where school textbooks may be cheaper.
[0] http://news.ycombinator.com/item?id=2949932 [1] http://www.raspberrypi.org/?page_id=2 [2] http://www.amazon.co.uk/school-textbooks-Books/s?ie=UTF8&...
By some HN comment standards, if that were really true, they'd be selling a $25 version of TAOCP.
(All these mentioned people who have access to school/family computers they can't play with because of the risk of breaking? They could use QEMU or VirtualBox and Linux right now).
Except that if you're the kind of person who doesn't have enough knowledge to set that up for your eight year old, are you really going to let them try and do it themselves?
There's a big difference between "Hey mum! My new teacher gave me this massive manual: can I install a whole load of programs you never heard of on the family computer?" and "Hey mum! My new teacher gave me this instead of a textbook. Can I borrow the tv to do my homework?"
It also skips the whole 3rd world scenario.