I can only understand it as a matter of theology. That is, in the LDS faith, infertile couples may be given the opportunity to give birth in the afterlife. Married couples in the LDS faith are commanded to have children, and it is possible to imagine that if they are able to, but refuse to do so the marriage will be limited in the afterlife.
This would certainly provide backing for religious marriage to follow such a pattern, but I don't think it provides a convincing argument for how this should relate to civil marriages.