When will it really expire?

Who determines the appropriate expiry date (or “expiration date” in American English) of a product (particularly a food item)? Have you ever wondered if your can of Coke will remain bubbly for another year as indicated on the expiry date? Well, I have. And I tried to dig up some info on this topic:

Nothing Simple about Food Dating, Expiration Dates or ‘Use-By’ Dates

Do Food Expiration Dates Really Matter?

Having researched these resources, it seems to me that the expiry dates tend to be on the conservative side. Are manufacturers erring on the side of caution or is that a legal requirement? Is there some kind of magic formula or is it just guesswork for different product types?