I wonder if age and the concept of marrying for love has anything to do with it? I mean, I can honestly say although I still deeply love my husband, in hindsight it might've been wiser to stay off.
Maybe age and religious influence in my case. Cause my religious upbringing (and his!) said no x, y, and z before marriage. And I wanted to take our relationship to the next level. So I pushed for marriage. Now, I think we would've been just as happy having those things without the title of marriage, and without the guilt of religious condemnation.
A curious thought crossed my mind, what is the purpose of open marriages? It comes to my mind mainly because of a recent House eipsode with a couple who were both into the porn industry, and very happy with having open relations. Apparently, they were still very connected and in love with each other and believed in the need for someone "always being there."