Respect and a healthy dose of fear. Fergie had it in spades. Because of that, no player would dare give less than 100% for him.
I don't think Jose has that same quality. If a manager with no previous connection to the club, who I knew will probably be out the door soon, who has disagreeable tactics and an arrogant character got on my back, I'd likely think, "Well **** ya" and feel demotivated. I'd still play for my own pride but not for him.
Giggs has a different problem. Although respected for his achievements as a player, as a person he's too nice/quiet. Soon as he's out of earshot after a bollocking I'd be laughing, "Oooh Giggsy, probably not getting any from his sister in law."
Keane is the one with that Fergie-esque fear factor - the palpable tension when he enters the room, that slight menace behind his gaze - it's what makes players sit up and take notice, it's what makes them react to his words. He demands respect, 100% commitment and the players know in an instant what will happen if he doesn't get it - it's black and white with Keano. He's also captained United to the lot (though he plays down his achievements) and the players would accept he's asking for the same effort that he once gave to United.
He'd get the maximum from the players and then some, how it was under Fergie and should be at United.