Coats of arms are not awarded to a family or a name, but to an individual. This is why there is often more than one coat of arms associated with a given surname. In England, direct descent is required for any heir to have the legal right to bear his ancestor's coat of arms.
The bearing of coats of arms is not regulated in most countries, including the United States, thus there has been a proliferation of "family name" companies offering histories and coats of arms for a given surname. While there is no reason we cannot enjoy the decoration of a coat of arms associated with someone centuries ago who shared our surname, we should be aware that this is all that it is -- a decoration.