It's all about how the rock gets to you. Your Fiji live rock might start out with the most diverse set of life on the planet, but I can assure you that most of the rock we in America receive from the Pacific (and other "wild" sources) endures conditions that make it unlikely that much beyond bacteria and some coralline survive to your tank. The TBS I have received has been stored and shipped in water pretty much for its entire life outside the Ocean, and the diversity of life on it is unsurpassed - you just aren't realistically going to get more life on any live rock unless you go to the ocean yourself (and that isn't necessarily a good thing all the time - you get the good and the bad).
Now, the diversity of life on the rock is going to be limited to that which occurs naturally around Florida, but most "wild" live rock, at least in the US is just a barren pink piece of stone in comparison.
Dave