I was thinking they are on the PLANE. Nothing that was on those planes, or on those floors during the fire, would have survived with its exterior remaining recognizable. These boxes are designed to protect the data on the inside through some pretty severe conditions -- they are not designed to protect the exterior paint jobs through these sorts of conditions. Which brings us to another problem with this story: the boxes are designed to be located by transmitting a signal which can be picked up by crash investigators (i.e. they are not designed to rely on their external appearance to be found). If the data in these boxes was still intact, and if the exteriors were still recognizeable, the transmitters would most likely have been working as well (since they too are designed to withstand extreme conditions), and federal investigators would have been making a beeline for the boxes in the rubble -- not sitting around waiting for some firefighters to stumble upon them.
The story just doesn't hold water. These guys found something they THOUGHT were the flight data recorders, but were almost certainly something else.
Wrong. I personally picked up items in the Pit that were from the floors that were hit and were easily identified as such, not many but some.