A Manager needs to be able to organise, to maintain an overview, to understand the broader picture, to direct people to specific tasks. He (or she) should be able to document needs and results, to be able to communicate effectively with the staff he manages and with his superiors. The latter requires a knowledge of the business, the company structure and objectives, of budgets and finance (and its reporting), even of commercial law. It requires an understanding of psychology and motivation, or team organisation. Take a look at the syllabus for an MBA or an MSc or other higher qualification in Quality Management. A manager does not necessarily have to be an expert in the tasks his department or team actually perform. Authority comes with the position.
Conversely, a Leader needs to lead, not necessarily to manage and direct. He (or she) has to understand the technicalities of the task to be performed, to be able to carry it out (or, at least, to take an active and leading part in its execution). A good leader will be followed. He will be respected and hold power (authority) through his ability and personality, not through his position. A knowledge of management (as for a manager) will probably be useful – but not essential, for his value lies in his ability to add value. Of course, a leader needs to be able to communicate and motivate, but a lot will be done by example rather than instruction.
A manager will usually be judged on his (or her) ability to work within constraints; conversely, a leader may be judged on the way he (or she) breaks out of constraints. To a manager, constraints (which include policies, procedures and other rules) may be seen as providing security; to a leader, they become a challenge. A manager works within the system, a leader may often be seen as the system; the manager uses the ideas and theories already existing whilst the leader develops new ones.
With the route to the top of an organisation often being through the management chain, should we be surprised if a company lacks leadership at the top?
This is far from exhaustive and there are certainly overlaps in the two roles; each needs an understanding of the other but, for many organisations, there needs to be better recognition of the differences. This will then lead to more appropriate appointments and training, and more reasonable expectations.