App reviews are not a guaranteed advertising venue. They are there for the reader, not the developer. The fact that an app doesn't work on iOS 7 is relevant to anyone using iOS 7, whether or not it's an official release yet. As the article says, the iOS 7 beta is pretty widespread at this point. I don't think you can have it both ways; if the beta is in that many hands, then the feedback is useful for potential buyers.
Unfortunately, I'm guessing many of these reviews rate the app poorly as well. That's a much more legitimate complaint, and I assume what the author really wants to curtail. I think restricting reviews is the wrong way to go though. If you really can't be bothered to fix the issue until launch, then stick something in the description telling people that the iOS 7 version will be live on launch day. If enough people are complaining about it in the meantime to make a significant difference in your app's rating, then I'd take that as a pretty clear sign that you should consider fixing the problem. No one is forcing you to rewrite from scratch, and the vast majority of apps are going to update existing codebases just fine instead.