Case studies in MBA education?

Most case studies taught in Bschools follow a problem solving approach. But in real life, I think most of the energies of people who run businesses go into identifying the problems themselves. Most guys running a company just see symptoms or effects of some cause or problem that they are unaware of. Falling market shares in spite of heavy advertising spends, for example. A marketing guy may see that his efforts (read time, men and money) are not bringing results. Can he expect that someone from the sky would tell him what the core issue is and place that problem so conviniently on his platter (just like a Harvard Business School case study does in a well worded 5 pages document). When you do not know the problem , what do you solve?

If MBA education is supposed to teach you how to manage a business, shouldn't the stress be more on identifying the problems than on solving some problem?