When you think about the word manager, you realize that there's an explicit meaning that has no flavor of leadership in it at all. Manager has the connotation of handling "things", which is why it is often interpreted as someone who can complete tasks or handle budgets and resources (yes, including human resources). None of this implies that the person given the position has the ability to deal effectively with people. Finding a leader amongst people who know how to juggle resources is rare.

So, is leadership development needed? Absolutely. The well-rounded manager has to be able to do more than just shuffle cchess pieces; they have to inspire and show through example. When they achieve that balance of leadership and task control, they will excel at all.