As usual, Neil Gaiman says it better than I can

According to the Bureau of Homeland Security, New York Has No National Landmarks That Might Interest Terrorists. "That was a key factor used to determine that New York City should have its anti-terror funds slashed by 40 percent--from $207.5 million in 2005 to $124.4 million in 2006." The official list omits..."The Empire State Building, The United Nations, The Statue of Liberty and others found on several terror target hit lists. It also left off notable landmarks, such as the New York Public Library, Times Square, City Hall and at least three of the nation's most renowned museums: The Guggenheim, The Metropolitan and The Museum of Natural History."

I keep finding myself wondering whether there's a little footnote in the report somewhere explaining that New York did once have a National Landmark, but some people flew a couple of planes into it.