I have a question. What type of behavior from the player are mimics supposed to elicit? I mean, assuming this problem was fixed and mimics were indistinguishable from items, to really deal with them effectively it seems like you would need to 'test' every new item lying on the ground with a missile attack or equip an amulet of free action before they moved adjacent to said item to avoid sudden random death.
It's kind of like insta-kills from invisible traps in the early game. The problem obviously isn't that early game deaths should never happen, the problem is that there should be a meaningful conversation between the developer and the player that is being carried out through in game events and the player's reaction to them. So, if something bad happens to the pc, the developer is saying "don't do that again, do something else next time instead." But in these sorts of cases there is no longer any meaningful message being communicated to the player, because the previous statement becomes "don't do that again, do something else next time instead (oh wait, you can't)."
And I think that when that meaningful conversation breaks down, that is when players start to go to the FAQ's, or scum for herbs, or whatever.