Hi Joblot - not to get them completely off the hook, but companies in the WTC did take quite a few steps. I worked in the WTC several months after the 1993 bombing (and left several years before 9/11). Many things were revamped and changed from the first bombing. Co-workers told of hearing no instructions because the public address safety system didn't work, and creeping down the smoky stairwells in near-total darkness, helping elderly/handicapped folks who couldn't walk down on their own.
After the '93 attack, a beefed-up PA system was installed, glow-in-the-dark strips and arrows were placed throughout the stairwell (every step). Security in the lobby kept non-employees from entering the elevators (except those going to the observation deck/Windows on the World). Co-workers told me that prior to that, tourists would sometimes wander around, and homeless people would sleep in some lobbies.
When I worked there, fire drills were a regular event - timed to see how long it took everyone to get up from their desks and walk to line up in the hallway (the idea being that the building's PA system would direct everyone on what they should do).
Now, that said, few people took fire drills seriously - they were a routine hassle for most people. Also, the WTC was a huge building, and right across the street was a fire station. Every day, several times a day, firefighters were entering the lobby, going up in the elevators with all their gear to check out false alarms. Someone smelled a funny smell, someone thought they smelled smoke, and it wasn't uncommon for fire alarms to go off errantly.
So, fire drills and false alarms were seen by many as a hassle, and when the alarms would go off, most didn't bother to stir from their desks, but would wait for the PA system to kick in and say it was a false alarm, return to your desks (I admit to doing this, too. Also, I didn't know where alternate stairwells were - stairwells were avoided because re-entry was locked except for certain floors, and because the elevators were so fast).
Reports I read said that, among other things, the PA system was knocked out. Some people who called 911 or building services were told to return to their desks. Others never considered it to be of concern to them - along the lines of another false fire alarm, etc. A lot of people never got their head around the idea that what was happening in another building/on another floor was a direct threat to them.
That said, others took threats very seriously - just read a very interesting book about Rick Rescorla (mentioned in the book "We Were Soldiers Once, and Young").
This book, "Heart of a Soldier," tells about Rescorla's military career and how he went on to become head of security for Morgan Stanley Dean Witter.
Rick Rescorla site
He had a very good handle (almost prophetic) on the threats that faced the WTC, and was able to evacuate several thousand of the firm's employees, although he and several others died in the building's collapse (he went back into the building to look for some missing employees).
So yes, there were more things that the companies could have done, but with the notable exception of a very few people, no one "in charge" grasped the potential threat would be much different from what had already been faced, and many employees were habituated to treat safety procedures/lectures as a waste of time and a joke.
My two cents
Dave