Only one floor failing would do the trick. It's no more bizarre that this would fall straight down than it would be if you dropped doughnuts down a broomstick.

And it would fall almost at freefall speeds? I know there was a lot of mass up there, but the rest of the floors seemed to be pretty strong. One would think they would slow things down some.

By interfloor areas I meant the layer between each flor that has ducting, conduits, pipes, etc.

And what about Building 7? A different construction, wasn't it, more conventional? But it came almost straight down, too, from what I could see.

According to the Pop Mech site Peter referred to:

NIST researchers now support the working hypothesis that WTC 7 was far more compromised by falling debris than the FEMA report indicated. "The most important thing we found was that there was, in fact, physical damage to the south face of building 7," NIST's Sunder tells PM. "On about a third of the face to the center and to the bottom — approximately 10 stories — about 25 percent of the depth of the building was scooped out." NIST also discovered previously undocumented damage to WTC 7's upper stories and its southwest corner.

That doesn't sound like the kind of damage that would lead to a vertical collapse.

Just things that seem strange.