Actually i'm pretty sure modern cars are fly-by-wire or whatever you call it.
Steering is still mechanical (wth power assist, but if that goes out the linkages are still mechanical).
Baking is still mechanical, except in regenerative braking systems where it's a hybrid - there's a few inches of pressing the brake where it doesn't engage the mechanical brakes, but engages the electronic regenerative braking, then it hits the mechanical braking if you press harder. If the power goes out, the mechanical braking still works.
Gas is mostly electronic throttle these days - not mechanical at all, and is the core of Toyota's problems (both the pedal, the floormats, and now the software are shown to be at fault).
But the big two - braking and steering, are still mechanical linkages.
There are some larger vehicles (think semi tractors meant to haul 40+ foot trailers) that have electronic braking (since it's already decoupled by the hydraulic system) that actually perform better than the older style because they account for overall vehicle stability control - which is fun on a big rig.
Newer cars with advanced stability control can actuate the brakes for you, on a per-wheel basis, but again - the brake pedal actually forces fluid into the brake cylinders if all else fails, so it's still a mechanical system.
Eventually we'll get there, but it'll be a long slow slog, and given the setback that Toyota has shown with one relatively simple system, we're probably going to take longer to get there than we otherwise would have.