Have you actually *read* the article you have posted? It's a good one indeed. Especially the last paragraph. The author is warning you that it's an ERROR to believe that 'The North Tower's Spire Turned to Dust'.
If it was as fragile as you pretend, it should have been crushed by the collapse front as the rest of the building.
And your occurrence doesn't explain the huge amount of basically intact core columns that could be seen in GZ. See the sat photo you have posted, or you can also see also a good amount of core columns in this one:
http://commons.wikimedia.org/wiki/File:September_17_2001_Ground_Zero_01.jpg
Which, by the way, also shows the damage done by WTC7's uncontrolled collapse to an adjacent building.
All these columns are on top of the pile because the core collapsed after the building did.
And that isn't explained by thermite.