Actually, he was going to retire after Princess Mononoke, but then Yoshifumi Kondo, the lead animator at Ghibli and one of the people who was supposed to succeed him, died suddenly in 1998. He keeps saying he's going to retire, but honestly I don't think he believes anyone else will measure up to his vision of what animation should be. Miyazaki's a pretty strong-minded guy. His opinion of the children of today's Japan, and modern anime, is not flattering, and most of the snippets of interviews I've heard or read actually show him as pretty pessimistic. Japanese values have been shifting and it's got to be uncomfortable for someone of his generation. One of the few criticisms that has been directed his way is that he's out of touch with today's cultural values. Not that too many people in the media in Japan are willing to criticize Miyazaki. He's even more of an icon there than here, and being less than complimentary can get you in trouble with your editors.
Chihiro at the beginning of Spirited Away was based on the daughter of a friend of his, and was supposed to represent modern ten-year-old girls. You'll notice that she's very different from most of his earlier heroines, most of whom would be considered strong role models for young girls (and something of idealized representations of girlhood). She morphs into a more standard Ghibli heroine by the end, though.
One of the reasons I'm looking forward to seeing Earthsea, when it is released, is that it wasn't directed by Hayao Miyazaki himself, and I'd like to see the Ghibli art style with a fresher director's touch. I love all the Ghibli films, but there's definitely a certain predictability to them. Grave of the Fireflies and Whisper of the Heart both had a more real, down-to-earth feel to them which was probably due to Takahata's influence (another reason I'd love to see Only Yesterday). It's not just the subject matter. Grave of the Fireflies would've felt more realistic anyway due to its subject matter. Whisper of the Heart is one of my favorites because the characters feel far less rooted in fantasy, despite Shizuku's story sequences, because their actions feel more naturalistic. Shizuku's not some fantasy heroine, she's the type of ordinary teenage girl who dreams of being the type of fantasy heroine she writes about. Less of an ideal and more of a real girl. It's refreshing, and I really wish there were more characters like her present in the Ghibli films.
I don't dislike Miyazaki. His main female characters are all unfailingly strong women, or are by the end of their film: active, confident, brave, smart, strong-willed, and caring (to varying degrees, true...San probably starts off as the most un-Miyazaki-like heroine of the group), without the sexualization that nearly all other strong female characters go through in anime. There's just a certain sameness to nearly every movie he heads up, and it'd be nice to see more variety from him.
