But that's exactly the point - Hamilton may just have had a slow exit on the straight and made no attempt to allow him to re-pass. The stewards will be investigating whether he did play by the rules or not by analysing the data from the car. It's not as easy to make decisions like this as you think.
Except for the fact that Ron Dennis contacted Charlie Whiting straight away to check they had carried out the yielding of position. As far as the race director was concerned they had done everything correctly.