It looks like the assertion brought forth by Popular Mechanics and other debunker sites isn't that the steel melted, but it became so weakened by debris from the twin towers and lower-story fires that it couldn't support the weight of all 47 stories. Which I got to admit, does make some sense.
Now, if they have an explanation for the BBC's early knowledge of the building's collapse, the firefighters' at the scene talking about a "secondary" explosive device within the building, Larry Silverstein on record stating the building had to be pulled, the building collapsing in perfect free-fall, etc......