This thread is giving scenarios that are completely out of proportion, too. No rust monster ever gets to strike effectively more than once. The usual reactions I've seen from players after they first experienced a rust monster run along the following:
- avoid the rust monster
- send the characters with light armor and non-metal weapons forward to take care of it
- cast
Charm Monster
- distract it by throwing it some coins, a disposable dagger, or any other scrap metal. Some even collected the weaponry from slain monsters to that effect.
Not once in the last 18 years have I seen a fighter go "naked" after a rust monster encounter, and I use that little classic more than others, because I actually like it. They might have lost a sword, or their shield, but those were all losses that were easily remedied. Shopping trips to the nearest village that take 8-10 hours of real-time gaming, or even more than one session?

Makes me wonder if I'm not simply playing a totally different game. If it's not the whole group that goes shopping, and each for rare stuff, shopping doesn't even take 30 minutes of real time. And if it's a low-level dungeon crawl, it's usually satisfied with "Okay, it takes you 2 hours to trek back to the village. The weaponsmith is all too happy to sell you a new longsword, since you pay with good gold. You decide to rest at the local inn for the night, and after your morning activities (cue wizards learning spells, clerics praying, etc.) and 2 hours of marshing back, you've returned to the entrance."
Another thing...it's patently funny to read people complaining about "save or die" effects being no fun, but at the same time seeing D&D turn characters into more and more effective death-dealing killing machines. Mid-level characters that can dish out 50 to 70 points of damage are effectively the same as a magical "save or die" effect, except that you don't get a saving throw, the attacker must hit you with an attack roll. If insta-kill is "no fun", and lost equipment is "no fun", and inconveniencing the character beyond one encounter is "no fun", it really makes me think D&D has turned into a game that's focussed on the "one encounter" philosophy. And it's no surprise that a lot of players and DMs feel that new players are being coddled. "Hey, I wanna go up against dragons, ogres and other monsters, evil wizards and supernatural horrors...but if that includes the risk of being incinerated with one puff of flame, or losing my precious weapon, or being afflicted by some permanent nastyness that takes special measures and long time to cure again, count me out."
Of course it's nice to have a new variant of the rust monster than works in different ways...but if that is a demonstration of the new design philosophy, why don't we simply integrate Save Points into the game where people can save their current game status before they continue down the dungeon? Should be easy enough to do with computer RPG software as it is by now. Simply save the character files, make a snapshot, and if the encounter wasn't satisfying enough, return to the snapshot and repeat with better knowledge of what lies beyond.
To quote the NPC with the most silly name ever, Bargle the Infamous: "We all take our risks here, down in the dungeon."
Edit: At least one good thing came out of this thread...I've read up on the 3E version of my beloved monster, and decided to simply go back to the older version of the monster. If it hits something metal, it rusts it away. If the metal is magical, it gets a chance at resisting the effect. And if the monster was successful in rusting something away, it simply stops its attacks and starts feeding. Because inherently, it's a peaceful little creature that simply wants some food.