The multipath from the Empire State Building and the barriers that the Midtown skyscrapers create lead to Pulse's weakened signal in Midtown Manhattan and areas directly across from it in New Jersey. Even then, a lot depends on location. I was able to get Pulse on my tiny Radio Shack radio with a clear signal in a hotel room at the Hotel Pennsylvania, right in the shadow of ESB (albeit with the antenna fully extended).
It may actually be possible for them to move up to the ESB though but it would almost definitely require a power reduction as well as some tinkering with their signal pattern to protect Channel 6 in Philadelphia, even after the switchover to digital, as they will be using Channel 6 for their DTV broadcast after the Feb. 2009 switchover. As an example, I believe that the LPTV on Channel 6 in Chicago managed to move to the John Hancock Tower, which along with the Sears Tower, is home to Chicago's FM and TV stations.