Yes, and same can be said of MBB which are brand management companies more than consultancies.
The reason they keep getting sales? It's all to do with clients taking the safe option (ever heard the phrase "no one ever got fired for buying IBM"?). Clients put excessive weight on consultants having undertaken identical work for identical companies elsewhere - something that naturally comes with size. It's an easy qualification barrier to erect, and doesn't require that buyers understand the work or engage in the consulting process. These firms also benefit from a strong brand and perception/reality that they employ a clone army - letting clients believe that any work done anywhere in the world, at any point in the past, by any individual consultant, can be replicated by any other consultant in the firm.