It doesn't only happen for marriages that last a short time, Nancy. My mother, when she was workiing, had a boss (who was a real bastard, apparently), who, because he knew one of the Bishops in the Cleveland Catholic Diocese, got his 25-year, 3-child marriage annulled so he could marry his young mistress.
Well, what goes around comes around-three months later, he died of a massive heart attack at his desk at work-found by my mother, of course.
The Catholic Church allows a payment to get an annullment, btw, which, to me, is a form of hypocrisy. I differ greatly with The Church on it's stance on divorce. It will forgive a murderer who confesses to a priest, but won't forgive a bad marriage via divorce.