At least in the UK, and I would suspect (but can't confirm) in the States, there are two systems which *must* have a mechanical connection that works in all circumstances: the brakes and the steering.
That usually comes out as a direct shaft all the way from the steering wheel to the steering rack, and a hydraulic circuit from the pedal's master cylinder directly to the brake callipers - in fact, two independent circuits are mandated.
Steering is easy, although most people are surprised about just how much muscular effort is required to turn the wheel at low speeds with no power assistance in most front-engined cars, but I have a certain distaste for the idea of, for example, self-parking systems: that implies a servo system that's significantly more powerful and could have nasty consequences if the electronics decided to do something you didn't expect - they're a step away from a basic feedback-controlled system.
Brakes, on the other hand... an ABS system works by interrupting the pressure lines feeding the brake cylinders. An active traction system both interrupts and applies brake pressure independently of direct driver input. This is something with which I am not happy and I would much prefer to avoid driving a car so equipped - I've worked in electronics for far too long to expect things to work as designed forever.
The problem is that both systems are, for different reasons and for different people, necessary. The steering assistance is required for financial reasons: front wheel drive cars are cheaper to build but make the front of the car heavy; many people would find driving, and particularly low speed manoeuvring difficult without it (though I prefer a much heavier control feel than is generally available these days). Auto parking? Why? What happened to learned skills?
And the same really applies to skid/slip control systems: they're now on pretty much everything... and yet, a competent driver will never find himself in a position where either is required... so they're excess weight and excess cost and excess complexity, and encourage poor driving skills - because the brakes are like, magic, aren't they?
And yet... these critical systems are designed so they can be updated (good design) without a direct electrical connection (stupid beyond measure) even though there is a mandated electrical connection directly to them.