Browsing through these forums again, I see that this post is still at the top... I've just entered "controlled demolition wtc" into google because I was curious what the word out there was, and among the top links is this one:
http://www.debunking911.com/pull.htm
I've not been reading everything, but it seems that there was a controlled demolition, yes, but by the firemen because they wanted to keep fires in control and to stop them from spreading. I'm satisfied with that answer, no mystery here.