Ohappyday:
Thanks for those very interesting comments. I guess I just assumed that God delivered the entire Mosaic law to Moses in the mountain. But considering the hard hearts and the difficult ways of his people, Moses might have requested concessions.
Another thought comes to mind, too. The divorce provisions are found in Deuteronomy that Moses delivered 40 years after the wanderings just prior to the Israelites entering the "promised land." (Deut. 1:3) Moses had experienced 40 years of trying to solve the complexities of keeping his people under God's law. Certainly, marriage then as even now can present many problems.
As you said, there is no definitive answers. But this does seem reasonable. Thanks for sharing.