I think personally, at issue was the fact that a CR 3 creature has such an insane power, and not so much the power itself. It instantly konks out the fighters deffense and ability to do damage, without much in the way of a save. That really doesn't sound like a CR 3 power...
It's fine (somewhat) if you're playing with old hats with a lot of metagame knowledge... "I uhh... decide now would be a great time to practice my 10 foot pole skills..."
But with newbs who will only discover the ability AFTER their gear has been wonked? Big effect. If the figther suddenly looses his damage ability, suddenly every other CR in the dungeon just gets higher.
Now, I realise that in a dungeon yeah, hit sappens sometimes... But again, is that power a CR 3 power?
Thus, the redesign. Not to make the game any less challenging, but instead to make the rules flow a little more orderly... (A CR 3 is always a CR 3 and a CR 20 is always a CR 20... if you wanna go ahead and tack on a CR 20 ability to an Orc, that's all you... but the rules should be safely assumed to be what they say they are...)
As for the 10 minute thing... At first I had a similar reaction to a number of people in the thread "What??? How do you explain that!?!" But then I thought, ok so durring those 10 minutes the sword (or whatever) is brittle, but not enough that it cannot be used. The fighter just has to compensate, and thus the penalties.
Afterwards, when the effect is gone, the fighter has simply resharpened the blade or similar to fix the weapon. (Sort of how the rules assume characters in their down time clean and oil their weapons and stuff...)
If the Rust Monster gets enough of it's saliva or whatever it is that does the rusting, on the thing, then the damage is irreperable (is that spelled right?) and Rustie the Rust Monster has himself some lunch. Yum.