I guess I'm either an unreasonable person, or in the minority of reasonable people. To me, "stable" does not imply happy; it merely means unlikely to change or collapse. A "stable building," for example, would be one that is structurally sound, not one that houses wholesome activities or makes people happy.
Also, just look at every single chart and data point mentioned in the article. All are about one dependent variable: divorce rate. Even if there is room for reasonable disagreement about the implications of the word "stable," reading the article makes it abundantly clear which definition was intended.
I'm assuming that most people are more interested in happy marriages than stable ones (at least before they've made the commitment). Now the marriage traditionalists might not. (This seems to be supported by at least one or two of the people posting here. But at the same time, one of them still mentions "happily-ever-after".) Even going back to the Declaration of Independence we see "pursuit of happiness" mentioned prominently in even those much more conservative times. Going significantly farther back than that I can start to see how "stable" might be significant, but in this day and age "happy" seems like a safe bet.
On the other side we have the word "divorce", which everyone agrees means "definitely unhappy". However, "not divorced" is definitely not a sufficient condition for "happy". The word "stable" is in the middle and can go either way. In one sense I agree it has a strong similarity to "not divorced". But in another sense, I think a lot of people read "stable marriage" as being very similar to "happy marriage". So to the extent that stable == happy, it's missing the point of the actual stats. And to the extent that stable != happy and a good proxy for not divorced, it's missing the point of what people really want out of life (and marriage).
This brings us to your response to my other comment, and there I think you're right on the money. The purpose of marriage is the main issue here. In my mind, the traditional view is synonymous with "stable" and not getting divorced. And the fact that the OP is talking about "stable" and "divorce" in the way it is suggests that the traditional view of marriage is a strong influence (although maybe my religious background is biasing me here). But none of this is very relevant if "happy" is what people are really after.
> I'm assuming that most people are more interested in happy marriages than stable ones (at least before they've made the commitment).
That's a very reasonable assumption. But it's also reasonable to analyse divorce rate data. You can't just assume that anyone studying marriage will only be studying how to keep marriages happy. I don't see any claim that this study is the ultimate study on marriage.
Also, just look at every single chart and data point mentioned in the article. All are about one dependent variable: divorce rate. Even if there is room for reasonable disagreement about the implications of the word "stable," reading the article makes it abundantly clear which definition was intended.