My A8 is showing 142k but wouldn't be at all surprised if it's lost at least 100k somewhere along the line as it's generally in much worse shape that my C4 A6, which has a genuine 294k on it. I'll be photographing the 300k moment!
High mileage is no issue on a car that has been maintained. My son's Seat Arosa 1.7SDI (S is for slow) has done 167k (and only eaten 2 gearboxes), both my 90's were still going strong at 170+k and likewise our Mk2 GTI.
Keep changing the oil and timing belts and it'll be fine
Nick