I think you're ABSOLUTELY right, this is one big reason for no satisfaction in these designs. Everything else looks relatively pathetic. Sadly, and yet understandably on so many levels, what may stop this from happening is fear. How would you answer the concerns that it would be a total target for future attacks and that people would be afraid to work in them? Maybe the idea mentioned above about them being "hollow" or not inhabited above certain floors except for the observation deck is a really good one.
All of these proposed designs are so much wasted time anyway when there are perfectly good designs already on the books, and that is what was there before, perhaps with an added story or two, and improvements such as can be made to enhance safety and security. But the best security is proactively eliminating the terrorists where they live.