You are missing an important difference too
A druid who wears prohibited armor or carries a prohibited shield is unable to cast druid spells or use any of her supernatural or spell-like class abilities while doing so and for 24 hours thereafter, but a druid is not prohibited from wearing metal (prohibited) armor, however. There is no cheese, not even borderline cheese.
Yep, as long as the player doesn't utilize any of their druid abilities for 24 in-game hours, I'd be satisfied. But I'd like to see the player who would actually do that...
I compare this to playing chess with someone that is playing by checkers rules. I'm not just going to smile and humor the guy because I think he's a simpleton. I'm going to kindly and carefully explain how the rules go. Games have rules, and rules should be abided by.
But I think those saying metal armor is ok is misunderstanding something.
To begin with, the list of metal armors available to a few types of druids in the Forgotten Realms which Badelaire supplied a link to (which is without a doubt the most lenient, contradictory, core-rules-be-damned setting out there), was limited to elven chainmail and light chain. Neither of which is in our loot tables.
Therefore, any metal armor that could theoretically apply to an atypical druid, isn't even available.
Hey! Hey! Has to look like plate! Cheese~!!!
*resists urge to start up on that topic*