The amount of people who misunderstand the term "Gambling" amazes me. Gambling requires a bet with the hopes of increasing your monetary gain in some form. When you buy a pack of cards for any TCG, you get a random assortment of cards. X common, X uncommon, chance at 1 rare. This is NOT considered gambling, and in the same way the containers are not considered gambling. (Despite how people wish to call it such.)
You are buying a container that has a random loot table. You are not betting on an outcome in order to increase your wealth.