This is absolutely the case (source: I'm a former pentester in charge of the social engineering).

SE had two guarantees for every organization we were hired to pentest.

* We would get the information/access we wanted

* It would be easy

Chris is a pioneer in this branch of the industry and has done a great job of highlighting the importance of social engineering through his research, books, and the CTF at Defcon (which is awesome to watch if you get the chance).