THe problem I see with many of these kinds of discussions is that people confuse simplicity with elegance. Not that simple can't be elegant, however, the reverse does not have to be true. A clock is very elegant, however, I don't think anyone would argue that it's simple.
An excellent example of this is the difference between older version of energy drain and 3e's version.
Prior to 3e, an energy draining creature hit you and you lost x levels. You can't really get much simpler than that. Hit, drop levels, go to half way through the level, press on. That's much simpler than 3e's gain a negative level with its encumbent penalties, followed by a saving throw the next day for a permanent level loss.
However, it is far less elegant. The game comes to a grinding halt because of a simple attack by a spectre for example. Say I toss a spectre into an encounter in an adventure in 2e for 6th level characters. The spectre hits the fighter twice and then dies. The fighter is now 2nd level adventuring with a group of 6th level characters.
Now, because restoration was pretty much beyond the grasp of a party of that level, either for price or whatever reason, the campaign comes to a grinding halt. You have two choices. Either the party babysits the 2nd level fighter until such time as he becomes useful again, if he ever does, or the character is retired. This means that a minor encounter with a creature throws a huge wrench into my entire campaign. Bob, the fighter player, doesn't want to sit on his hands for the next five sessions until he gains enough xp to pull a little bit more weight and I'm fairly sure the rest of the group isn't too thrilled with having this albatross around their neck.
Compare that to 3e mechanics. Same fighter gets whacked for 4 negative levels. A sixth level party has access to lesser restoration most likely, so, while those negative levels are dangerous (since a third hit means dead PC), the effects aren't particularly far reaching, nor do I have to rewrite my entire session (or more) because of a single creature.
To me, the 3e mechanics for level drain are far more elegant. Level draining undead are still very dangerous. A small number of hits and you have a dead PC. However, they don't wipe out several weeks worth of gaming while we figure out how to get Bob useful again.
An elegant mechanic works very well and doesn't screw up other things. Simple mechanics might be elegant. OTOH, they might be extremely inelegant. The rust monster was another example of this. A throw away monster that could have huge effects far beyond a single encounter. It's not like a rust monster is going to lead to lots of plot or interaction. It's a bloody big lump. It doesn't talk, it doesn't scheme, it doesn't do anything that a trap doesn't do. Yet, using a rust monster can radically alter my campaign.
So, I don't use rust monsters. Before 3e I could probably count on one hand the number of times I used level draining undead. Both for the exact same reason. They are mechanics that, while very simple, caused far too many compexities in my game.