Thanks Captainplaystation.
It seems to me that the flight planners will normally have you there with an ok amount and that if the Captain decides on a bit more that they are not questioned about it , but do have to write the reason for it.
So the only problem will be with Captains who make poor decisions at the flight planning stages and First Officers who don't have the spine to say " actually I had a slightly higher figure in my head because of XYZ"
I am not saying that the crews of the four jets concerned made poor decisions, they all landed ok and sometimes things do get a fraction finer than you want due circumstance.