I'm glad for what you did include in the bibliographies and I can understand why material like shareware and Traveller web pages are not included since they come and go very quickly.
Yes, the ephemeral nature of the things is the other reason. (Software is particularly hard... yes, I know I could probably even now play the MT adventures under some kind of emulation, and I'd probably love to, it's just time, time, time... (as I was just saying to someone).
Of course it may also be some kind of inherent librarian snootiness about non-book material. I'd like to think not, but there's nothing quite like a simple physical object I can pluck off the shelves, browse through and 'relate' to very simply! (At one time I considered not including PDF only material in the bibliography. Hah!)
tc