As for the bug reports in the review area, I imagine this is for a couple reasons.
First, it's the easy way to give feedback to the developer. I don't know of a way to provide feedback within the App Store architecture other than through the review process. Any other method has a chance of being painful. Being forced to sigh up to some developer site bug tracking system, and then getting sent email after email notifying you of every status update. Of course, I also have to search around for how to contact this particular developer with a bug. There is no easy method that I know of to do this.
Secondly, it's a sure way of getting the attention of the developer. Reviews directly impact the developer, and an email directly to the developer might not get a response as quickly as you want.
I'm not saying either reasoning is correct, or right. I'm not judging the reasoning. I just imagine that's the two biggest reasons for using reviews for bug reports.