I think it's obvious, the tank is not the asset at all, the crew is. You can build a new tank far faster than you can re-train a good crew. Pretty much all MBTs have the same basic features... Challenger, Leopard 2A6, M1A2, Merkava 4, T-90... long gun, heavy armor, high speed, good optics & sensors, good comms. Now except for the T-90, which I don't think has seen combat yet, does anybody know of a case of any of these tanks ever losing crew members? I know some M1s and Merkavas have been disabled, but I haven't read of any crew losses. I do remember one story of a M1 driver having his tank wrecked with a multiple 105mm shell IED, but they carved into the tank 6 hours later and the guy was still in his position without a scratch, just really bored.
(Quoted for truthfulness)
If you consider the way the Iraqi's employed their Tanks' in GW1 and II, you'll see that tactics, training, and intelligence have a lot to do with it too. You can't just drive out onto the modern battlefield in a tank, and expect to get within sight of the enemy and be invulnerable. Nobody's built an AFV yet that can do that. The Iraqi's dug their tanks' in, but in bare open sand (at least, that's what a lot of GW I pics' show) and although the hulls' were protected, the turrets' were exposed, due to a lack of any other kind of cover. They just died in their revetments, for the most part sitting ducks.