No, its better than that IMO. For example, I did a rat-men bestiary spread for a recent project (read Skaven) and I could have used all the rat-adjacent entries fomr the main book in full if I had so desired. I ended up just using references to conserve space, but I think it's more useful than...
Change it? I wouldn't. However, I do love to create extra little bits to bolt onto it (perhaps that's what you mean anyway, IDK). For example, my most recent project adds firearms and an additional playmode for serious injury.
I've published a bunch of stuff for Shadowdark and I've found the license very easy to work with. Referencing the main rulebook for existing rules is exactly the way to go.
It may be, but it's also the case the the markup goes down as you move up the tiers. The high tiers are essentially wholesale prices (as Kelsey explained it).
I went for the premuim slip case and a copy of the new premium rule book. Which has three ribbons btw. I couldn't resist a pretty book with three ribbons.