A king move can be the one strong move in a position, but let me be more clear. Early into the game your king is usually pretty far away from the action, so even if it is the best move, moving it usually doesn't affect things in a direct enough way so as to have a massively positive effect on the position. It's possible, it's just not very likely. It's only in positions where the king is really getting into fights with the other pieces where it becomes likely a king move is the one strong move.

These kinds of heuristics doesn't need to be perfect to give you an edge.