Maybe they work together so well because Wash knows when to give and when to take, when to speak and when to keep his mouth shut. He knows that there is a morning every April when Zoe rises early to watch the stars, hands clenched so tightly together her knuckles stand out, like she's praying to an unmerciful god. It's some kind of anniversary she doesn't share with the captain, so maybe it's not from the war, and it kills Wash to watch his wife stick out her grief alone, straight-backed and facing the black. But there's nothing he can do.
Well, maybe not directly. He acts normally all day, since she won't take any pity or even sympathy, thinking the entire time, and by night he has a joke for her so funny it sends her into tears, tears that end up falling for something else, and he holds her until they fall asleep in each other's arms.