Patent cases are definitely going to include expert testimony on what someone with ordinary skill in the art knows or believes, but other kinds of court cases (or types of participation in a case) don't always have a simple opportunity to introduce expert testimony -- like writing an amicus brief.
So it would be pretty awesome to have the Book of Tacit Computing Knowledge somewhere.
The term of art here (as used in patent law, for instance) would be "person having ordinary skill in the art". Something like that (if you don't encrypt something in a network protocol, it can be sniffed) is "obvious to a person having ordinary skill in the art".
But yeah, that does make it difficult to cite sources for them. And in particular, it's difficult to throw the book at someone who doesn't take those things as obvious when there's no such book.
Another "obvious" thing that I don't know a citation for: it's impossible to store a piece of information in a binary such that it cannot be read by a person who has a copy of that binary. (Practical corollary: there's no such thing as a piece of information that's too secret to include in an Open Source driver, but that can be included in a binary driver.)