Yeah, I agree with you. wouldn't be too hard to do. This computer on a stick seems to be essentially the same idea Knoppix pioneered.
I guess it's nice that someone's mass-producing them, but Google shows lots of pages on how to roll your own if you're so inclined:
http://www.google.com/search?hl=en&lr=&q=linux+boot+usb&btnG=Search
(Memo to self: Try copying Knoppix ISO to a USB drive later)