The real point of good live rock is biodiversity. There's dozens of genera of creatures that will come in on the rock, call your tank home and be happy to eat all the poop of all the other creatures. You get all that by taking rocks directly from the real coral reefs and shipping them to your pet store. Now take the Jersey shore--there's some biodiversity there, but what beneficial creatures are really going to come into your tank via a rock from the beach?
Of New Jersey, George Carlin once said it is indeed the Garden State, that is, if you're growing smokestacks. Not to pick on New Jersey, but everywhere on the eastern seaboard factories, powerplants and refineries are dumping nasty particulates into the air. When it rains all of these are stripped down into rivers and out into the sea. Let's not forget sewage--Every week here in Rhode Island the paper prints a map of where the poo line is in the bay. Everywhere north of that line you don't want to be collecting clams to eat!
Not to say that there's anything wrong with collecting local crabs to feed your critter, but I'd say after all the heartache we go through to mix our salt with ultra-pure water, it doesn't make a lot of sense to grab rocks from one of the most polluted places in the world: the continental shelf!