He's mad at you. You are sure it's his fault, but you know he's mad and you want him to feel happy again, or at least stop being mad at you. So you stay up an extra two hours past your pumpkin-turning-time when sleep should, by all accounts, be re-humanizing you and you slip into that little nylon/silk thing he bought you over the holidays and make sure you're well showered and try to win him back to your team.
You stroke body, mind and ego, you grovel, verbally and physically, you release, with ooh's aaaah's and forgiveness and try, with intimate pleasures, to move on from the fight/disagreement, spat, friction.
Or this: He's tiled the bathroom floor and it cost hours and hours in time, sweat, loud radio music and tears. The result is absolutely beautiful, cost effective and a source of great accomplishment. Of course he'd like to be taken out to dinner, but maybe he'd like something else as well? Something you don't do every day?
As we know, sexual intimacy can be important for any relationship to promote that warm fuzzy feeling afterwards, the bonding, the togetherness, the glow, the "falling in love all over again" the "you and me against this crazy old world" sensation. Why do we use sex to apologize, or to reward or thank our significant others during tough times?
The argument for reuniting over sex is not complex. It feels good. It's a way of reconnecting. As many women know, women usually connect easily in their heart center, or their emotions, and men connect most easily through sexual intimacy.
This is not true for everyone and certainly not completely true across the board without exception; but if a woman loves a man and this is somewhat true for each of them, they know that reconnecting in this way can do wonders for a healing, a show of appreciation, a getting-back-together-after-a-fight sort of bonding.
That being said, sexual bonding should not be a replacement for dealing with the deeper issues involved in the argument or for really taking the time to verbally and emotionally thank someone or show appreciation in non-sexual ways.