From the interview:
Because agents found themselves more and more providing services that they never needed to in the past: a cover approval, correcting cover copy, editing, spellchecking authors manuscripts, marketing, and other tasks that should be the publisher’s, but the publishers either can’t or won’t do some of these things. They keep pushing the burden of responsibility back on to the author. And the author, if the author can’t do it or is helpless or doesn’t want to, the agent has to do it.
A joint production of Digital Book World and Astral Road Brand Media: http://www.astralroad.com/