Good question about vocation. I have met several Catholic people who have told me they feel no desire to marry. They hadn't been "scarred" by any experience, didn't seem selfish, just didn't feel "called" to marry.
I think the difference is if you choose not to marry for the sake of GOD, rather than lack of means, opportunity, or desire; believing that God is "calling" you to a single life in the world as opposed to just ending up that way. Not sure if you could really refer to that as a vocation in the traditional sense of the word.