Well, those are like solo sessions where only one player attends. In most other RPGs - Call of Cthulu (BRP) or Traveller (most editions) combat ability is just one skill among many that a character can have, it's not necessarily the most useful skill - certainly not in Call of Cthulu - and a knowledge-based or diplomacy-based PC will get just as much screen time as a combat-based one. This definitely isn't the case in D&D. In D&D combat ability is THE defining characteristic of a character, everything else is ancillary.