In the early days of the Apple App Store, feedback could be given for applications much in the same way you can for products on Newegg, Amazon and many other sites to help people make a purchasing decision. Given that word of mouth is one of the most important advertising tools, this is a good incentive for developers to make good software. Unfortunately, Apple found that their reviews were often tainted, getting both positive and negative reviews from people who hadn't actually used the application in question. The end result was Apple prohibiting non-customers from submitting feedback, though it still left a massive amount of reviews left.
That move came in September of last year, and now Apple has finished cleaning up the mess by deleting all reviews posted by non-customers. Reviews submitted by current customers are still intact, though it did leave many developers with significantly less reviews to use as references for their software.
As easy as it is to criticize Apple over some of their App Store policies, this one is a pretty fair move. If you aren't an actual Apple customer, or haven't even purchased the application in question, it's not very fair to be offering feedback on it. There's always room for corruption in any feedback system, such as developers reviewing their own products or paying for positive ones, but by at least this way they are reducing those possibilities. In this fashion, do you side with Apple or do you think it is unfair for them to prevent non-customers from leaving feedback?