Being a strictly trad gamer and iffy on games with super-focused premises, I wonder where games like (old school, TSR/OSR) D&D and (Classic/Mongoose) Traveller sit on this spectrum? Though they are fairly open at first glance, the rule sets often imply premise. D&D goes on and on with rules about exploring underground complexes, opening dungeon doors, checking for traps and rolling for random encounters and surprise and reaction. Traveller goes into detail about starship mortgages and arbitrage trading.

Compare with, say, Rifts — which just gives you character creation, setting, monsters and assumes you’ll manage to order all of it into a coherent game.