If Mascherano didn't work hard off the ball he'd be useless. It's what his game is about. The point is solid enough but the example isn't the best.
Hard work can be coached...to an extent at least. A good man-manager can get it from a player not renowned for it, Mourinho and Eto comes to mind. Wenger doesn't seem able, or doesn't want, to do that. But the players whose game is defined primarily by their work, Kuyt and Park are good examples, you can't turn your average player into one of those. It needs some natural talent of having an extra lung or something, most players would be keeling over after half an hour if a manager made them do it. If this wasn't the case there would be an awful lot more distance runners.