Demos share some qualities with prototypes.
1. They offer an insite into early game development.
2. Some demos are not available to the public.
3. You can't consider them released titles.
4. Its impossible to find any type of accurate listing on them
5. People used to throw them out.
That being said they aren't really protos but I think many people who are interested in prototypes find demos a cheap and easier to find alternative to proto collecting.
BUT.....the question is should we include discussion of demos in this forum? If you are against it please speak up so far the only voices I hear are those who are for it.