I was messing with my neighbor last night, sending my sov & some champions over to her city and taking out units I found wandering around outside.  I found some structures that were built outside of the city walls, and I wanted to destroy them.  I sent my group over to the buldings, but they just sat on them, and when I moved them off the buildings were still intact.  I don't know if there's some kind of requirement that has to be met before you can destroy structures that I just didn't do, but I'd like to be able to take those out. 

If a tech is required to raze structures (I understand there is one for razing cities) then maybe that needs to be looked at again?  Personally, I wouldn't think it would take much know-how to just knock something down.