Honestly, it's many years since I read these books so my memory is a bit hazy, but from what I remember Boukreev's book was a response to what he saw as Krakauer's criticism of his actions as a climbing leader during the fatal 1996 Everest disaster.

Roberts is more like a historian with the perspective that Herzog perhaps wasn't so heroic after all but instead, despite poor leadership and reckless decision-making, was saved by his companions that were the true unsung heroes of the expedition.

The first book is a rebuttal, the second is trying to reveal what really happened many years ago.