I grant your skepticism.

But we in the US have not had a history of suicide terrorism. Generally, US terrorists want to live to terrorize another day. Whereas in the Middle East, there is a darn near constant stream of suicide bombers/mine-seekers/whathaveyou. It's in the mindset, that Allah will grant paradise to someone dyiing in his cause - whereas in the largely Catholic/Protestant US, suicide is seen as a sin.

And I think there really are too many people involved to have been a domestic suicide operation You might find a few nuts willing to commiit suicide for a cause, but enough trained to take over and operate four *large* airplanes? While flying a jumbo jet is said to be almost so easy a kid could do it, with auto this auto that, it's not that easy a task to manually steer a jumbo jet into the World Trade Centers, as apparently they did.
My pet theory is that whoever did it infiltrated the country more than a year ago, got jobs as baggage handlers, and waited for the signal. Reason I suspect baggage handlers? Otherwise they couldn't have coordinated the attack; if they were flight attendants or pilots, they would have been all over the US at unexpected times.

Oh well, we'll find out more in days to come, I hope.