It is increasingly true if you notice that a woman will have sex with man she loves even when she doesn't like it, and a woman won't have sex with the man if she doesn't love him.

Sex if woman's way of expressing love, and unlike men that is able to separate sex and love, for most of woman sex is love.

Hence to answer TS question, if a wife isn't excited in the bed after marriage. Chances are she never loved the man to begin with. He is just an additional accessory in her life.