In that case, what difference does it make whether they do it on a Boeing or an Airbus? I fail to see your point re- the 'hijackability' of the design; which although not foolproof, is certainly a great improvment over what most 747s have.
The concern isn't over "highjackability." A jet carrying 800 passengers, as opposed to 400 passengers, is a pretty attractive target for terrorists. They like to get a lot of "bang for their buck," inflict the most damage, and kill as many people as possible. That is why they chose their 9-11 targets instead of a convenience store in Hackensack, NJ. There are lots of ways to bring down an airliner other than highjacking -- bombs, shoulder fired missiles, maintenance sabotage, etc.