I guess that one incentive to change it from earth to poison damage is immersion and logic.
Appeals to realism are not great as the first argument for something. It's not an inherently bad argument, it's just that everyone has different personal views about which specific parts should be changed for the sake of realism, and which parts should be left alone despite being less realistic.
So I usually try to find a logical argument based on something firmer than realism. In this case, I am unpersuaded that removing earth damage from wands and staves and putting poison damage in its place for the sake of realism is a positive benefit.
My argument against the change is this: because loot you find is very highly based on RNG, so it can be a while between finding good weapons. If you only have poison-based wands/staves, that eliminates your basic attack from your arsenal for a very large number of encounters on this undead-infested island.
(I know this discussion has monopolized the thread, sorry about that. This is of course not the only complaint I have, I've got a long list which I'll post in another thread.)
