If it's random, it's fair, and hence, balanced.
It's not like Mario will get double the healing from food items, or Snake will have a homing super scope. Sure, there were minor variatons in some of the items in Melee, like how a character used the beam sword, but nothing that ruined the balance of the game.
The random explosions are awesome.
I kill myself because of it all the time, and I still love it.
It's just some more incentive to throw a box/barrel/capsule at someone, instead of at your feet. If it has items, they're closer to them. If it goes boom, they go flying. If you throw it at your feet, you get easy access to delicious items 7/8s of the time, but 1/8th of the time, you pay for that privilege.
It was perfect.
Predicting when and where items will occur and be easy/hard to obtain adds one more layer to the game. You can use items offensively, defensively, as bait, as distractions, whatever. It allows you to play in so many different ways.
When items are off, you have one task, and you go at it like a sex deprived teen.