The security isn't as great as you claim. Wish that it were. Worked on Wall Street post 9/11 and there were trucks that got there, with noone really knowing what was on the truck or who was driving.
Rode the ferry with a trader from the floor who described to me how a Pakastani with a backpack got to the floor of the Exchange and when security asked him how he got there and what he was doing there he said that he didn't know.
Saw an Arab riding the ferry and getting off and then getting back on again and taking it the other way.
This person was riding it for the point of riding it and observing operating procedure.
What I am describing here could easily have been trial runs by the enemy in at least two of the above cases, possibly.
At best they were mere lapses in security.
I worked on Wall Street for 15+ years and the level of security you are describing was put in place after the 93 WTC bombing. Post 911 there is only on way to get a vehicle close enough to do any damage (no I won't say how) and to get that close you will be stopped and inspected before time. When you get close (but still a little too far to do major damage) every single item on the truck will be scanned.
Now I'm no way saying it is impossible, but it is not as bad as you are making it out to be. Also add to this the "Wall Street" these days is not really necessary to do the Exchange's business and I would think that there are better targets in NYC if you knew what you were after.