They are not the same. Read the SRM and there is a section on compatibility. http://circuitco.com/support/index.php?title=BeagleBoneBlack
DDR3 is cheaper than DDR2
I removed the FTDI and HUB from the board, a big $$ savings.
Instead of building in lots of 2000 we are building in a big lot of 100,000. Higher quantity, lower costs of parts.
eMMC is cheaper than a separate SD card.
Assembly process is automated, lowering assembly.
Testing is automated, lowering the test cost significantly.
Gerald