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.
This is probably the kind of "technical" stuff BW might throw around to get it away with it. If you're not a lawer, you should be.
It doesn't matter if what people are after is wealth in the real world or a coveted item in some game. They will be beting with their real money against low chances in hopes of getting what they crave for (which you can bet are not 20 upari crystals)