Actually, I was reading some time back that an increasing number of people postpone marriage but not children. They feel "ready" for one but not the other. Yeah, ridiculous. If you can't handle an adult, how will you handle a child?
These relationships are completely different and not really comparable. It would be like saying if you can't commit to another adult in marriage how can you be a dutiful and loving daughter to elderly parents?
Marriage breaks down far more frequently than does child and parent relationships.