I dunno, I think the Tank is very vulernable. Even in WWII tanks could be easily destroyed by a varity of methods from aircraft, mines, AT equipped infantry, artillery not to mention other tanks and AT-platforms, and this was BEFORE the advent of the AT-Missile. On top of all this all tanks now have to deal with Helicopters which are ideal tank hunters and specialist tank killers such as the A-10 Thunderbolt II and AH-64. Even Iraq has showed that even a car packed with explosives is capable of disabling all but the most heavily armored of tanks. Thats not even mention all the MANPORTs and Technical mounted systems out there.
I think the days of the traditional manned tank are limited, but perhaps unmanned where they are smaller, less expensive and frankly more expendable is the key. Just an idea...