Electric steering, too

http://en.wikipedia.org/wiki/Power_steering#Electric_systems

Several years ago, a friend bought a BMW M6 the year they came out. A few days later, he noticed when the tires were pointed straight forward, the steering wheel was not centered. He took it to the shop, and they told them "that's a software bug".

That's the result of a combination of two things: aircraft don't often have one of the major problems that cars have (dense traffic and other obstacles), and that the problem of dissimilar surfaces was solved, for aircraft, by making the surfaces more similar. Cars instead have to be able to negotiate a variety of terrain.

So, safely automating cars is a harder problem, but not because the car itself is a more complex vehicle.

Fly-by-wire avionics go beyond "just" self-landing and auto-pilot (and these are no small accomplishments!). In fly-by-wire aircraft, when the flight controls are moved, it's the software that calculates how to move the control surfaces to achieve the desired result. Also, modern fighters are often designed to be inherently unstable, to achieve greater maneuverability. So even in level flight, the software must calculate and order constant tiny movements to maintain stability. These movements happen dozens to hundreds of times a second, and must take into account factors such as current speed, attitude, air flow across the aircraft, etc.