The Ground Zero Clean-Up Was Much Faster and Cheaper Than Expected

There are many articles that say this, here is one example.

The article explains that part of the reason the clean-up was cheaper was because the "bath-tub" that had the foundation for the towers, was much less damaged less expected. This is consistent with what Wood and Reynolds are saying here.

I wonder if the clean-up was quicker in part because there was much less steel than expected to haul away.