If you buy the game from release day onwards, you will have to buy the culture pack online separately. It's for pre-order only. I'm not entirely sure how it works, I've never pre-ordered anything(though this might be the first time that I do

), but there might be some codes you get. Maybe there's just a database that checks the serial number of the game you have and compares it to a list of pre-ordered games.
The problem with buying retail on the fifth day is that lots of times these aren't new copies, but returned and resold ones(that's especially true with the latest FPS titles). The profit from those goes to the retailer, not the publisher. Pre-order is apart from other things a way to ensure that the profit goes to the producer, not the seller/reseller.