I think it really depends on the person buying.

I think car people will be more conserned about the mileage and service history and less concerned about the year (Personal opinion)

Where as non car people may care more about the year and the money they have to fork up at the start.

So for that reason someone may think say a 08 520d with 180k miles is not worth much because it has high mileage where as others may look and think, Ohhh i can have an 08 5 series the neighbours will think were great.

It depends on the car too though, generally I wouldnt look twice at a higher than normal mileage petrol car but might consider a diesel with higher than normal mileage.

Its kind of the same as people buying lesser quality cars because they can buy newer.
eg my mother and sister inlaw just last year went out and bought 2012 peugeot 308s because they were the newest car available in their price range instead of buying something a little older and better quality as i recommended.

Thats just my take on the situation.