Not a fan of zynga, but tiny tower and others do that too. It seems pretty standard for games to prompt users for reviews.
They're offering additional game features in exchange for 5 stars, not merely prompting users for reviews.
Do other apps do this?
What are you quoting? The picture you post says "Give us a FIVE-STAR rating! Higher ratings mean more features!" I take this to mean they will develop their higher-rated games more than their lower-rated ones. Where does it say you can have more features in exchange for a high rating?