This is of course the addicting nature of collectable games in the first place. That small but persistant possibility that what lies, unknown, in there could have great value. The smart people among us know that the odds in general suck and it's far better to sell it to saps who will pay more money than it's worth to open it and take their luck. There's a reason why for old magic boosters and baseball card packs, the unopened ones are worth almost more than some of the high priced cards in the set.
I had a thought recently that what I should do is wait until CCGs die completely, and then buy up hugely discounted boxes of boosters just so I can cheaply have the satisfaction of rare and ultra-rare hunting. God knows I have enough CCG packs for various games just sitting around here.