As I have been one my entire life, I am quite comfortable with the concept of only children. It's not odd to me that a child has a decent relationship with her parents.
This does seem odd, however, to other people.
When asked who's going on vacation with me, I respond, "Oh, my parents."
I get a variety of odd looks which only continue when I finally say, "I'm only child."
If I said, "I'm going on vacation with my parents and my brother," would that seem less weird? Is it the vacation with the 'rents or the fact that there are no siblings that throws people for a loop?
I know of many "grown" children who still travel (and/or live) with their parents, and it doesn't matter to me whether those children (well into their twenties) have siblings or not.
Perhaps, to the outside world (and by "outside," I mean those people who are not part of my regular social circle), the weirdness of it all is a combination of the two things:
1) I get along with my parents and travel with them
2) I have no siblings
Even in "modern" California, it's still odd for some folks to process that not everyone grows up with siblings, and in an increasingly "me" oriented world, it's even harder to believe that someone actually gets along with her parents.
Oh well, I've never claimed to be normal!