Given I'm one of the few on this board who actually admits her status as being in an open marriage, I think I'll take this opportunity to jump in with my two cents as a form of counterpoint based on my experience.
To start, our marriage is not a trial separation or business association nor have we lost any intimacy to our marriage. Actually, I thought we were even closer, if that was possible, due to our commitment to honesty and full communication with each other and everyone else involved, just like the straight-up swingers. I don't see this changing, even if someone spit out the study or numbers showing that my marriage is more likely to fail than a vanilla marriage or a swinger marriage. It can and does work for some...
There's certainly failure of marriages associated with swinging or poly as there are with open marriages. A screwed up relationship isn't going to survive swinging, cheating, poly or an open relationship arrangement. Someone who moves into an open marriage or swinging because they are bored, or want sanctioned cheating or unfulfilled already has issues prior to doing this. It's certainly no different than married couples that enter swinging to try to fix their marriages or who decide they are poly in order to sanction their cheating somehow.
The reasons why people go into open marriages, polyamory or swinging to me is more indicative to the potential to successfully maintain the current marriage or relationship. Expectations for/upon entering into a non-monogamous also seem to play a huge part. The state of the marriage or relationship before entering into an alternative arrangement is yet another huge factor.
And this is what seems to have been revealed by the OP, that there may be factors out there that may indeed indicate problems already that may indeed end in a broken marriage. But it isn't going to be necessarily because of an open marriage. We could substitute any number of alternative relationships in place of the term "open marriage" and the potential for failure will remain the same because of the potential underlying issues that exist before even entering the alternative sexual relationship arena.
I know this is your opinion, and my response is not intended to be an attack. I read this, and my first thought is who is to say that people in an open marriage are not enjoying this adventure together? When did proximity become the qualifier as to enjoyment?
Okay, I'll get off my soapbox. It was kind of lonely up there anyway since I'm in the minority position here.