The WTC towers did undergo a pancake collapse!
The floors then started progressively falling and piling on each other, in a progressive pancaking fashion, leading to the overall collapse.
Seriously, I think there is some basis to the pancake collapse model. This may be why so many scientists have been able to put the pancake collapse model out as an explanation for what happened on 9/11 and then not feel like they are totally lying.
But the key is that the pancake collapse just doesn't work unless the core is demolished.
Once you watch the 9/11 eyewitness DVD, you will see that all three WTC towers underwent essentially a conventional controlled demolition-- where there was an initial powerful explosion that took out the key support columns in the core. Afyter this, the structure started pancaking by natural gravity-- the outer walls couldn't hold the weight of the floors, and the whole thing gave way. The slowish early initial collapses of the top sections in the beginning of the WTC1 and WTC7 collapses was probably just the pancake collapse starting to gain momentum. Perhaps the first set of charges weakened the core, starting some downward movement, then the final set of charges took it out for good.
Conventional demolition is very similar-- there is an initial set of charges that weakens the structure and then the "killer" charges that cause the structure to collapse at near free-fall speed.
WTC2 was done a little differently-- maybe by mistake or maybe they were testing out the demolitions to see what they needed for WTC1, and thus only did some at a time. The 9/11 eyewitness DVD reveals there were eight or nine explosions right before the WTC2 collapse.