We're still doing fine. :-) My wife said that my contract expires after 50 years, then we'll see about re-upping it. I've still got 30-odd years to go, wish me luck. :-)
However, I'd posit that there's a big difference between two professional late-20somethings making a considered decision to live together for a short while before marriage, and a couple of teenagers right out of high school playing house for an indeterminate amount of time. This "study" likely doesn't think too much about that.
Should I still be looking for the other shoe to fall?
I agree with the age factor. I think commitment also factors in. Hubby and I had been in a committed relationship for 4 years before we joined households, and we knew it was a permanent arrangement. We just hadn’t gotten around to getting the piece of paper. Of course, when you’re in your early 40’s and 50’s, you’re a little more settled in your mind with what you want and what you’re committing to. At least, we were.