Your last two paragraphs hit on a point that more managers need to implement but are afraid to, because most managers think that if they make themselves redundant, then they'll be laid-off, instead of promoted.

I know of one manager in particular that is amazing at managing restaurants, but his problem is that he has to put in long hours to make sure the restaurant runs, and if he leaves on vacation, then the restaurant has often fallen apart (not to mention the years of increased stress levels it entailed worsened his cholesterol levels to the point he needed surgery). If instead he had trained everyone else to do his job, not only would he have had a ready supply of people to promote all these years, but he would also be a lot less stressed-out and maybe wouldn't have needed surgery.