Aren't the Israelis still using Super Shermans?
And, of course, the Sov, er, Russkis still have most of their old tanks. They use T34s as pillboxes along the Sino-Sov, er, -Russian border.
Real point is, the threat hasn't changed that much since 1970. Shermans were designed (shortly) before things like bazookas and panzerfausts (the precursor to the RPG) were introduced. The threat was small caliber AT guns (37 - 50mm). Under the pressure of WWII, the threat changed very quicly and when the Sherman was deployed it faced much more powerful weapons like the 88. As a result, they died a lot.
But, since the 1970s the threat hasn't changed much. Nobody has introduced a new level of tank-killing fire power, like, say, a railgun. Weapons have evolved, and so has the M1. There is hardly a comparison between the M1 and the M1A2. The M1A2 is a good weapon for the current era.
The Army SHOULD be looking at vehicles for low intensity warfare like it faces in Iraq and will face elsewhere.
http://www.globalsecurity.org/military/world/israel/army-equipment.htm
Not in any serious capacity. They may still have some stockpiled, but they are not relying on them.
I wouldn't argue that the M1A2 is not a good tank for the current era. I would argue that we can do much better in 15 years, nevermind 24.
And I would argue that the threat is evolving quickly. ATGMs are much more powerful. Top attack munitions will be widely available within the decade. While we are upgrading the intervehicle electonics substantially, the in vehicle could be improved A LOT. The point is to stay ahead of the threat curve. Waiting until we have to go to war with an outdated tank is not the time to start its replacement.