There is a difference between hoarders and extreme couponers that have a stockpile. If you watch both types of shows you'll see how the hoarders actually have a mental disease almost OCC in their behavior in wanting to save everything. Usually a hoarder's house is stuffed full with piles of random objects all over the place. They hold onto items without the intention of ever using the item (even if that is what they say). They usually have a fear that they will lose their possessions which is why they begin to hoard their items.
Couponer's stockpiles, on the other had, usually only have one room dedicated to their stockpile, and it is neatly organized by products and stacked on shelves. These couponers DO NOT hold on to their purchases indefinitely, as some posters seem to think, but rather are meticulous in purchasing only what they can use within the product's expiration date. Even some products that technically could be stored for longer periods of time (eg canned goods) are usually used within a reasonable period of time. Usually these couponers have studied the store's and manufacturer's specials and have figured out patterns in sales such that they will purchase only enough of a product to last them until the next sale for that product occurs. For example canned soups tend to go on sale during the winter esp. during the holidays. Thus couponers may create a stockpile of canned soups at the end of December to last them until the end of September when the soups go back on sale. You have to remember that couponers are doing this to save money, so there is a limit to how much they will spend on any one trip. Even "free" items usually have some cost associated with them, even if that's the time spent clipping those coupons or making the purchase. Therefore couponers won't make purchases of items they don't plan to use (unless they have decided ahead of time that their purchases are going to be donated to charity). It is a waste of time (and possibly money) to buy a bunch of cake mixes only to have to throw some away because they got old, or never actually used them all ever.