David Maister, author and professional services expert has a deep insight on his blog.
There is a widespread misunderstanding that good management means being "soft." In fact, holding on to the best and the brightest is NOT about making the firm less demanding: it is about making sure that the organization provides fast-track learning opportunties and (as Ms. Hymowitz pointed out) opportunities for people to take on lots of extra responsibility early. That DOESN'T challenge the business model of the firm (as some senior people fear) but it DOES challenge the security of the senior people. It means they must be willing to delegate more, and keep moving on to new things themselves, so that they are not the bottleneck to achievement.
When good people have to grow in their careers they want different things from their firm. Some might want flexibility, some might want a larger portfolio to manage, some new markets to develop and others might want to focus on new products and offerings. The common point is a growth in the complexity of work and things that challenge them.
This means leaders have to focus on innovation - because the development of the organization is linked to the development of its key people.