It's no secret that app reviews are important for app sales. Once you come across an app in the store, it's really the only way to customers can find out if the app is good or terrible. The problem with app reviews is that they are subjective. Maybe someone thinks $2 is too much for an app (as they drink a $4 coffee), but that doesn't mean the app isn't worth $2 to you. Whenever an app is updated, the reviews are 'reset'. While the old reviews are still there, the most prominent ones are the ones for the current versions
Whenever an app that you enjoy is updated, take 2 minutes and either leave a review or update your existing one. 2 minutes isn't a lot of time to you, but it can mean the world to the developer and other potential customers.