Actually, Rick Warren has been asked specifically about this quote. His response is that he stands behind it. So it wasn't the publisher, it was Warren that chose to use it. Imagine your church using this book, and a visitor who has a problem with pornography was attending, looking for salvation. He sees this quote, and thinks "Wow, these people accept Anais Nin!" That alone is enough to remove it from his book, but Warren refuses.
I just don't get it. Is he aware of Anais Nin's sordid background? He may as well have asked Larry Flint or Hugh Hefner - though I think Anais Nin may have surpassed them both in terms of depravity.