I am not the voice of BPI team, but I realized that DC is a better choice for development boards.
However, it is not that MicroUSB is bad, it is just that development boards should have more power for add-ons. With a MicroUSB plugged in to my phone when I am gaming the phone charges incredibly slowly b/c the game is power hungry. Note that the phone also does not have ports taking power from it like USB ports and stuff.
On a development board however the 5V 2A cannot cover all the power needs for the SoC and extension ports on the board.
One intersting thing to note is both the DC port and MicroUSB port are rated at 2A from the adapter. I guess the cable of the MicroUSB can account for some power loss and a higher amp rated DC adapter will provide more power.