I believe that executive employment contracts often predefine severance packages if one is fired without cause. The employee does not want to end up unemployed if he gets into a minor squabble with a board member, and the board does not want to pay out if the executive is caught supplementing his income through drug dealing.

Also, I suspect that it is harder for someone let go to claim employment discrimination if he is fired for supposed cause. However, further elaboration would require a law degree on my part.