Word comes from MacRumors that Apple is removing the 'rate on delete' feature from the next iPhone. Starting in iPhone 2.2, when an app was deleted a notification would ask the user to rate the app using a 1 – 5 star system. The reasoning behind the feature was presumably to increase rating participation in the iTunes App Store.
Many developers were unhappy with the system, as it skews ratings down. The system increases the number of negative ratings. Customers who were unhappy with an app, deleted it, and were able to easily rate it. Unlike those who kept the app and were happy, they would never be prompted for a rating, or worse, have to go the extra step of logging into the store, search out the app and rate it.
The rating system is currently enabled on the iPad.