If you're worried about what your child sees on the App store why don't you shut it off?
What I would say is that you should take off the App Store (in restrictions in settings) and then if your child would like to download an app you would need to navigate to it on the iTunes store, you can vet the app (and the comments if you really want).. download, and install via sync.
Unfortunately, whether you agree with the nature of the comments or not, you will find profane stuff all over the world and it's very hard to protect your child from it. I wish you luck on getting a reply from Apple, but, it is something that you could probably have avoided by taking action yourself - Whether the iPhone is touted as a gaming platform or not, that does not mean that all games are sunshine, roses and bunnies. Some people find Gorey games fun, some find racing games fun where you can run people over...
Besides, we have no idea when these comments were posted so, you have no idea as to whether Apple could have intervened. It's not impossible nor unreasonable to expect that Apple vet every single comment made before it being published, much like on these forums here.