Apparently, Blizzard developers have at least had internal discussions about treasure chests and keys. It's not a debate that must be limited to fantasy games. Lockers, desks, and ammo crates often perform the same role in realistic FPS games. The essential question is this: When loot is part of gameplay, is it better to control supplies by distribution or by access?
Keys and hacks are methods of access control. The player might be able to see where the loot is stored, but he cannot access that loot because the container is locked. Supply is determined by skill (such as hacking ability) or by meta-loot (such as keys).
Unlocked or open containers are methods of distribution control. If the player can see it, the player can get it. Supply is determined by the frequency and locations of containers.
Which would you use? or would you use a combination of the two?
Fable 2 has locked chests requiring silver keys to open, with silver keys hidden in fixed locations around the gameworld. This has two benefits: (1) the player is encouraged to explore, and (2) anticipation is allowed to build before loot is acquired. Unfortunately, I don't recall any loot in those chests being that spectacular, so the lack of access is more disappointing than exhilirating. And searching for silver keys rarely, if ever, leads to other rewards (even aesthetic rewards, like a striking view).
Diablo 2 has both locked and unlocked containers, with keys acquirable by drop and by purchase. The main problems here are: (1) keys are so common and cheap as to be mundane, and (2) locked chests don't always provide better loot than unlocked containers. Again, keys don't seem to be much fun.
Fallout 3 and Oblivion make unlocking loot containers a skill. The result is that loot frequency becomes an important variable to overall gameplay -- if you can't or won't pick/hack locks, then your character must make do with far less equipment and money. This is a better use of access control. Bioshock also uses this system, though in a more fluid way (allowing skill-augments to be swapped out).
I prefer distribution control. Diablo 2's gear and loot system, overall, is less about maintaining needs than discovering wants. It favors spectacular finds over mundane acquisitions.
Can an access system, like keys and hacks, be spectacular?