As you ascend the ranks of consulting and get to the top 3 shops (McK, BCG, Bain) it drops down to 1/20th to 1/30th. That is once you take into account the disparity between number of hours billed and the number actually spent doing the work.
When you buy consulting, you're buying a commodity. The premium is meant to insure you against natural variation, key people quitting, and so forth. Joe Accenture is meant to be interchangeable with any other Accenture consultant. A lot of the overhead is the extremely rigid, prescriptive methodologies that are supposed to make this possible. For multi-year projects, enough budget-holders believe that this is worthwhile for the entire Big Consulting industry to exist.