A guild bank with the assets I describe is not necessary, agreed. A guild bank though? Some central repository of a guild's 'assets'? Every PvE guild has one. It is necessary. The game is set up that way. Coins/Bijous in ZG. Idols/Scarabs in AQ. Wartorn scraps in Naxx. FR mats in MC. Elementium from BWL. Etc. Every single raid instance is conducive to having a guild bank and that is if individuals completely account for all consumables on their own.
There is no way to 100% safeguard your guild under the current system. I agree that splitting up the items amongst separate people definitely reduces risk and is something we should have done more of. Obviously we (me) fucked up and trusted the wrong guy. Why does it have to stop there. This is a solvable problem. Blizzard can tell what happened, where the cash went. Why arent they? Are they not obligated at all to do more than 'Sorry, tough shit?' These items in question have real value and 50+ people got fucked here.
Blizzard should either alleviate the need for a guild bank, add some real guild bank functionality OR do more to fix things when they break, as they clearly did in this case.
When someone's account gets hacked, who is to blame? My account has never been hacked and I would argue that the person being hacked ought to be more accountable than Blizzard. But Blizzard fixes that, or tries to. I know people who have been 'hacked' and they get their items back, eventually. Why wont they even look into the matter here?
Yes most raid instances prior to TBC had such a mechanic, although currently there has been no examples of this as yet in post expansion raids. Another difference is that most of these items had no tangible value towards the end of pre-expansion WoW(exluding bijous for people who still needed rep/enchants and maybe Elementium if someone wanted a TF/AQ weapon).
From your post I believed that these events transpired after TBC was released, when all of the items in question had almost no value whatsoever. If such an event had occured during the hayday of MC or ZG/AQ when such items were needed on a frequent basis it could be devastating but at this point it is crying over spilled milk.
Also as I alluded to earlier in TBC there have been no such token systems placed in raid instances which solves the problem of needing a central banker for such items as you said.
As for hacked accounts, the difference in this case is that you willingly gave said items to your guild banker, you never willingly gave your account information away to someone who was able to hack your account. The later is a flaw in Blizzard's account security which they take responsibility for by assissting you in character/item retrieval, the former is a flaw in who you trusted with an innordinate amount of materials, which is in no way a fault of Blizzard.