I think in most cases it has less to do with religeous affiliation and more to do with the compatablity of the couple. I was married to a JW for 18 years and we were just not very compatable with each other. Neither of us were truly happy. Turns out that being a JW was about the only thing we had in common.
A couple years after divorce, I met a great woman who was brought up as a baptist, I was already an exJW at that point. We were very compatable and have been together for over 10 years. We are both very happy. In hind sight, I wish the first marriage would have ended sooner, but that is not so easy in JW land.