Just to throw my two cents in.
First off there is nothing on the modern battlefield that can't be killed or as least disabled. To be sure there are some weapons systems that give this impression. Some Armies when everything is going IAW doctrine certainly can prevent the enemy from hitting its weak spots. However, this is combat we are talking about here and stuff happens during combat. In the scope of Steel Panthers/MBT the Challenger story would be a kill or at very least a heavily suppressed immobilized tank. Either way combat ineffective (except I'm sure it PO'd the insurgents involved)
A game I've played recently against Egyptian M1's, to be sure, I did spend a lot of time and effort winging rounds off their frontal arc. But at some point a kill/combat ineffective state can be achieved. This is usually using all manner of weapons including HEAT rounds. My point being I don't think there's much out of whack with the armour ratings as is.
I might mention as well that as good as the IDF may be, I'm sure their enemies while not as well trained and motivated differently, have come up with tactics that allow some successes on occasion. IIRC Merkva loses are pretty much a state secret for the most part. This is telling in itself.
These are my opinions and this is an interesting topic so let's continue on gentlemen.
