I'm sure they could have done that anyways. AMD kept backwards compatible sockets with the physically similar AM2, AM3 and AM3+, while increasing memory speeds,

I'm sure they could have done that anyways. AMD kept backwards compatible sockets with the physically similar AM2, AM3 and AM3+, while increasing memory speeds, introducing new chipsets, and introducing their Hex cores. I would prefer the option to accidentally buy an old motherboard and have my CPU not work at optimal settings than Intel's solution where the CPU won't work at all even though it fits.