Not to be too obvious, but:
Why is it that there are, largely, two groups of people in this debate.
The first sees the druid restriction, understands it for what it is, and are like, "Okay, cool, if other people disagree with it, then they can just houserule it."
The second attempts to make various arguments that UNLESS the rule is perfect, then THE RULE DOESN'T APPLY. Now, notice how these individuals (you are one of them) doesn't do the following-
State that the rule is poorly implemented, and therefor propose a solution to implement it, such as:
"If a druid attempts to wear metal armor, or use a metal shield, then he or she shall lose the ability to cast any druid spells; such loss is complete the instant the action is taken to wear metal armor or use a metal shield. Should this use continue, further loss of class abilities will continue at the discretion of the DM, and if a druid willfully continues to wear metal armor or use a metal shield, the druid will be forced to abandon his or her class and adopt another.
VARIANT RULE: If a druid attempts to wear metal armor, or use a metal shield, then he or she shall spontaneously combust, taking fire damage of 10d20 per round until the metal armor and/or metal shield is removed."
There. Fixed. You should propose this to WoTC as errata.