The whole idea of Marriage is Commitment. The whole idea of Shacking Up is to AVOID Commitment. Salt and Sugar may look a lot alike--but no matter how much salt you add to a pie you'll never make it sweeter; that requires sugar.
: I believe that couples who wait, are more willing to act with retropicity. Couples seem more eager to please, are flexible and most times willing to be flexible and consider their spouses ideas and needs after marrige. Rules are present that are not necessarily present before marriage. When you live together, you loose the excitement of the "new" and you can get lazy about your partners needs. There is no "commitment" to honoring vows when you live together without marriage. You are roommates with benefits.
This is simply my opinion.
I purchased your book Ten Stupid Things Women Do to Mess Up Their Lives
...this has indeed changed my views on multiple things, including cohabitating!