InApp Purchases: Why do you have to fetch a list of products before selling them?

ios InApp purchases: Why do you have to fetch a list of products before selling them?

Following this l开发者_开发百科ist: http://troybrant.net/blog/2010/01/in-app-purchases-a-full-walkthrough/

Why do we even need to fetch the list of products before selling them? Why not just sell the hardcoded id's we create for the app?

It's a bit difficult to sell a product without stating the price.