Definition of Managment Consulting 

I've modified the paragraph discussing the types of firms to use the more narrow term "strategy consulting" rather than "management consulting".

Managment consulting currently has a very broad meaning.  IT, intellectual property management, law, and accounting all involve choices that can have a profound effect on the opportunities and resources of an organization.  In current usage it seems that the term "management consulting" refers to any sort of consulting activity that

 has strategic implications for the future
 requires senior or upper level managment champions and buy in

To distinguish a Bain from a PWC we need to focus on difference between strategy and implementation.  Strategic IT, strategic IP management, and management accounting and other "new" forms of consulting all have a blend of implementation and strategy in common.

I think what distinguishes a Bain from a PWC is Bain's exclusive focus on the strategic elements of a problem.  Bain will tell you why you need to do something and some general ideas of how given your current resources but leave the rest to you.  Firms like PWC and  Proudfoot have built their reputation on taking at least joint responsibility for the implementation.