Is the M4 what was called an CAR-15 “Shorty” back decades ago?
It's the "grandson" of the CAR-15. Lots of major and minor changes since then. But still the same concept of making it shorter and lighter than the standard rifle. In urban fighting in Iraq, a shorter weapon is appreciated. Afghanistan has much more open range, there the demand is for supplemental weapons with more reach, like .308 and above.