Sorry to add to a dead discussion, I just had to say that ASUS support have constantly offered the wrong advice to me on this one. I have a Maximum IX board and distinctly remember official support stating that the antennas aren't for Bluetooth. This was repeated in a support request I made to ASUS recently, the antennas are not for bluetooth - I thought okay the antennas must be etched into the board.
However I just couldn't get it to work, so decided to buy some cheap 3rd party antennas and lo and behold, Bluetooth is working. I can't comment on Wi-Fi - Bluetooth degradation as I have Wi-Fi turned off, but both being at 2.4GHz and seemingly on the exact same antennas..... it seems like they're going down the route of flatly denying they did it 🙂