I think we've finally hit the threshold where a lot of adults would rather have animation, than live action with BBC-tier special effects. We've had about 2 generations that really appreciate anime, and have embraced things like the various Don Bluth masterpieces of the 80's and 90's, Heavy Metal, the Tolkien animated efforts of the 70's, The Nightmare Before Christmas, A Scanner Darkly... It's just a great medium that shouldn't be relegated to children alone.
Three of the longest running scripted entertainment shows in TV history are animated: The Simpsons, Family Guy, and South Park. All are definitely adult oriented.