If you start a tank with dry rock, the only bacteria that tank will have is from whatever bacteria is in your LFS tank from when you buy coral. A lot of his bacteria is from his wholesaler and remember his tanks received his fish in water that was treated with who knows what.
The bacteria we need comes only straight from the sea and real live rock is loaded with it in it's pores.
Of course eventually the tank will grow bacteria, but will it be the correct forms of the millions of types of bacteria there are?
you get bacteria in everything you buy. When you buy a frag it has bacteria. You purchase a clean up crew it will come with bacteria.
when you buy frags from different hobbiest you will have different bacteria. When you feed Live or frozen food it will have bacteria.
with patience dry rock will be live rock in time.