I have heard of this and one of the main reasons is that not only is it a big change for the recipent, it is a big change for the spouse. Life is so different after tx. The recipient's spouse is used to doing everything for the recipient and after, they aren't needed as much anymore for the household chores and everything else. It can make them feel useless and the marriage can go down hill. My husband and I have discussed this a lot lately. I used to have to have him do just aobut everything for me, we couldn't talk a whole lot because I would start coughing, and I was in the hospital all the time.
It has been a huge change in the 2.5 years since my transplant. I can now take care of my son, clean the house, do the shopping, drive myself everywhere, and I have not been in the hospital since March 2008. I still have him help occasionally but it is no where near the stuff that he used to do for me.
I think that these reasons are some of the reasons that marriages don't work after tx. I have been fortunate that we have been able to work through all of this and we are still together and going as strong as ever.