Whilst I agree that no one intends on divorce, I think in some families it is more of an issue than others.
Whilst I would never say that comment to anyone, there are elements that I agree with.
In my very traditional family, divorce is just not the done thing - out of my parents / grandparents / aunts / cousins etc there is not a single divorce. The closest divorce within my family is probably my nan's sister's daughter. For right or wrong, there is the view within my family that 'you make your bed and lie in it' - one aunt even survived domestic violence and affairs, but they have worked through that now and have a reasonably good marriage. Now I'm not saying this is right, but it is an attitude that exists. I know I thought long and hard about marriage as to my mentality it is a life long contract.
In contrast, one of my closest friends has parents who have divorced (and several aunts, and a divorced brother too) and she has a much more relaxed attitude to marriage. Her attitude is that while it is her intention to only marry once, if it doesn't work out, she'll get a divorce and move on. She is quite happy to take things as it comes, and openly says if a partner has an affair - she would leave him etc etc...
Now, I don't think either attitude is the right one, horses for courses and all that, but I do think that when people say 'I only intend to get married the once' they can mean every different things - so I don't think it is necessarily a stupid thing to say.
That said, I think people do say it all too glibly and that's why it can sound smug. I don't think it is something to be smug about at all, but in contrast, it is quite a fearful statement to make. One I wouldn't say lightly!