Hey, that's a good site. I'm glad you found it. All I could find in my quick search were a bunch of religious sites and the one I linked to.
This is the actual CDC study. Sweet.
Even if there is no causal relationship between living together and the higher rate of divorce, shouldn't someone who is living together take that statisitic as a wake-up call? There is a correlation, even if it isn't causal. Even this site states clearly that if you are living with someone before marriage, you have a 9% greater chance of getting a divorce than if you aren't. (So what does that correspond to, a 60% divorce rate instead of a 50% one for the general public? I don't know those numbers) Regardless of the reasons, that should be a warning to anyone cohabitating before marriage.
I would suggest that anyone in that position take a hard look at their relationship and motivations before getting married.
The website you link to has some pretty good advice for cohabitators who plan to get married.