In consulting it's typical to get paid a quarter of your billing rate, as a rule of thumb. I've seen places where it's a tenth tho'.
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.