I agree with you - absolutely. The potential for growth and perspective as a human being is innate - some people have more of it than others. Though those people with greater potential - an awareness that our experiences can change us - are exactly the kind of people who leave their comfort zone more - versus the author of the linked story who writes: "But when I thought about what it took to get there, the diapers, the soccer games, the braces, the tantrums, the whole enchilada, I knew that it wasn't for me." That was the kind of person I had in mind.
I don't know what drive you to that conclusion, or what makes you equate not having children with never leaving your comfort zone.
I know parents who are not "adults" in the grounded/perspective sense, and childless couples with more perspective than I can conceive.