I think that you're overthinking this. A monster's list of moves is not a comprehensive list of actions, it's just there to give you an idea of how they fight. Of course the goblin can stab with the spear. He can also trip you with it, damage your armor, throw it at you, and use it to keep you at a distance.
Dungeon World is not completely different than other RPGs. It just places a greater emphasis on the game fiction and uses a different method of resolving actions.
In DW, you describe a monster's attacks just like any other system. But where D&D says "he stabs your leg for 5 damage," it's just flavor. In DW, it means something. You can say "he stabs your leg for 5 damage, and you fall down." That's an attack! Don't get too caught up with the specifics, I think the whole point is to use your imagination. When a player's roll triggers a GM move, just narrate whatever you think should happen. Whatever makes sense, you'll know what to do!