I think you are wrong about the wife having nothing to loose. It is much harder to raise children alone than it is with someone else. Particually if your working at the same time.
Besides, in this senario who is doing most of the housework? Rather than instinct what may actually be happening is that the wife's workload has just greatly increased, she isn't getting much sleep because the baby is waking up during the night and she just wants some help.
@lemmein Oh, there are. I would be one of them. I don't wear jewelry or expensive things and would much rather a nice day/night together than some fancy gift. And, by nice day/night together that doesn't mean pricey restaurant. I'd be happy with a picnic and a walk in the park. :)