In the past, developers have complained that the prompt negatively affects their rating within the app store as users will only be asked for a rating when they decide to delete the app (ie. when they don’t like it). However, the iPhone OS doesn’t encourage users to give ratings at any other point (for example, for apps that are used frequently.
The App Store has a history of problems surrounding app reviews. A little over a year ago, Apple modified their review policy, stating that reviews can only be made on app’s which have been downloaded (purchased) by the reviewer.
Furthermore, the App Store has faced problems with developers “buying” reviews or making reviews using dummy accounts. This is commonly done by using “pre-paid mastercards”, allowing the developer to have many different iTunes accounts.