If I advertised a D&D game with no description, I'm under no obligation to include combat. If I advertised a classic, combat-saturated game, there's still no formal obligation...
"Formal obligations". Sheesh. Are you a GM for hire, with a contract or something?
Who gives a crumb about formal obligations? I want to know instead, in each of these situations - Are you doing a good job as a GM to enable the folks at the table to have a good time?