ACC in normal mode adapts the dampers to the road conditions and uses its range of adjustment. Comfort or sport setting just sets it at its extremes iirc. (excluding how it changes the steering weight too).
ACC imo is a complicated, but to most people also a worth while option.
I found that 18s gave steering kickback on roads i drive.
To answer the original question im not sure. I too remember a difference back in 2005 of the mk5 iirc. I remember a debait about it as someone on an american forum started a question about it on a uk forum. It had something to do with bumpstops IIRC. I remember the arguments

It would not suprise me if the mk6 just has a single setup, to reduce the amount of parts and costs especially as there is the ACC option on the mk6.