In the sense that they are the enforcement mechanism of the law it's true that they can probably just ignore the law to a point, but it's no use pretending that there isn't a legal stricture here.
(I'm a policy opponent of historic preservation, which is a major impediment to housing reform, but even I don't pretend that it simply doesn't exist.)
Agreed, btw - I think the only method of preservation should be market purchase, to force the right tradeoffs.