IMO it is essential for Jobs to do that in order to demand high quality and perfection. It is better to say things like that in the face of people rather than to smoothen the communication and then let them go or move them to different projects without explaining why. I would absolutely do the same thing in his shoes. It is the fastest possible way to get the message across. Now, this may be unpleasant and he may indeed show some lack of balance of temper but it may very well be on purpose. This is of course speculation on my part since I haven't met the guy and I have not worked for Apple.