Phantom,
As theatreguy pointed out they do. The benefits of having a building reach landmark status is that it makes it impossible for other builders to demolish it to make way for their own projects.
I do know for example, that all the Broadway theatres at least have landmark status at least as far as New York City is concerned. Which, like I said means that they can't be knocked down. If they were to have national landmark status then it would mean the same thing, just another layer of protection.
It should be noted that with the case of Henry Miller's Theatre, the only thing that had landmark status was the facade. The rest of the building didn't and that was why they were able to do with it what they did. Which was that they were able to keep the facade and to build a new theatre around it.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll