If you just want to blow something up there's nothing even all that special about "transportation". Planes are special, because they have an unusual characteristic; taking control of a plane gives you an extremely powerful weapon that you can point anywhere and deliver incredible destruction. There aren't very many other things that two or three people can do that will credibly take down a skyscraper.

As it gets harder to deliberately crash a plane and there's ever more drive-by-wire, though, that threat diminishes, and the airport threat diminishes with it. Hypothetically if planes were completely ground-controlled, there would basically be no reason for airport security at all... blowing up planes isn't that intrinsically interesting, really. There'd be a certain amount of inertia to the concept, but that's it. (Yes, I know it used to be done, but post-9/11 I can't help but think that terrorists would view that as a pathetic second-best effort now.)

(Though I'd appreciate some serious security around the ground control station, though. Taking over one plane is one thing... taking over "all the planes in the area" or even "all the planes in the sky" would be something else!)