Hi there! Thanks for taking interest in the game!
The 8s are actual 0s, so you will be always trying to roll under. We mostly use Roll20 to play these days, where setting up dice with values from 0 to 7 was very easy with lists and macros. Before that, we found reading 8s as 0s something that came naturally in the course of a player's first session.
Regarding balance, that was perhaps the main consideration. GURPS was, of course, an influence in terms of what to do and what not to do. Certainly, there would be no point in writing a 400+ pages book that didn't try to do something different than what is out there in the market. And we think it achieves that.
Setting books are basically system-agnostic affairs, but they delineate which modules must be used with them. Game masters will do the same when they create rulesets for their settings - each element in the book tells you, for instance, if it pertains to a specific tech level or BYTE RPG setting, so that you do not end up using it inadvertently.
Of course, you can put all 20 thematic modules into a setting. Would we advise doing that? I don't know. Would it work mechanically? Yes, it will, because, again, balance was the main consideration. For instance, when designing how aircrafts work, thought was put on not only how one aircraft interacts with another, but also what happens when it faces a land vehicle, or a starfighter, or a mecha, or a flying creature, or a person. All done in a simple, straightforward way, so no counting meters or yards, nor measuring wind speed. In the same vein, when designing the rules for supernatural powers, such as spellcraft, psychics, divine powers, mutations, etc, thought was also put regarding both what makes one different than the other, but also on how one stack against the other in terms of, again, balance.
Cheers!
