60 fps locked would have been near impossible, the game is visually amazing and that was just an Alpha, having the game stream all that data with AI, the high draw distance, effects ect would have been a pain in the ass. Bungie has always aimed for great art and worlds, sacrificing draw distance and effects for a higher frame rate would have been a mistake in my opinion, the amount they would have to sacrifice for a locked 60 fps without drops would outweigh the sales and effect of a visually stunning world.