ACC (Adaptive Cruise Control) on it's own is just controlling speed, keeping you a distance from the car infront via throttle and brake input so won't affect the steering wheel.
Like you say, lane departure warning will vibrate the steering wheel and input steering to guide you back to centre of your lane, but only works over a certain speed (40mph I think?). This is what's fitted to the Standard and Carbon Black specs.
Adaptive Cruise Assist (ACA) is what is fitted to the Vorsprung (or what you get if you option the Driver Assistance pack. It's ACC and what they're calling centre lane guidance these days - basically traffic jam assist and active lane assist combined so it'll work 0-130mph. You get the round wheel with ACA because it how it senses your hands are on the wheel is different. It uses capacitive grip recognition which is newer technology. They obviously haven't got this in a flat bottom wheel yet - maybe there's some complicated technological reason, or that they haven't got round to it... or just haven't bothered, who knows