[yummyfajitas]

The entire premise of "happy wife = happy life" is that your wife is making you happy. This premise is false. A wife can marginally increase your happiness, or make you less unhappy, but happiness is fundamentally something you need to create for yourself.

However, many people fake the "happy me = happy you" by making you unhappy. That is often within their power to do. Then they give you respite when you do what they want. If you don't know better, you might mistake this for happiness. From what I've seen, this is how "happy wife = happy life" (or in it's more honest form, "if momma aint happy, nobody ain't happy") is usually implemented.

When my wife asks me to do something, she's really asking me to show her that I love her. And when she gets that feeling, she's very receptive to the idea of sex. Win-win, as they say.

It might be a win-win for you, but many people dislike trading labor/money/etc for sex (even when the trade is implicit). Personally, I prefer sex which is freely given for the sole purpose of mutual pleasure.