Well, for the first time ever, an Abrams kit contains all the necessary parts to make either an M1A2, M1A1HA (USMC) or M1A1HA (US Army). The turret is entirely new and the hull has some retooling. The tracks are new as well.
If you bought a decent aftermarket upgrade OIF set to add to either kit, you'd probably pay over $15. Not that I'm defending the high prices, I'm just trying to put it into perspective.