We just got back from a week's stay at AKL, and yes... they only have bus transportation. I don't think it has anything to do with the cost or how much of a deluxe the hotel is. I think it's simply because it's so far from any other type of transportation. But we were not disappointed. The bus system is a breeze to navigate, and all of the destinations are clearly marked. We traveled to all four parks and to DTD (and once we even went and toured the other hotels) and the entire time we used the bus sytem. We never had to wait more than 15 minutes for a bus, and 3/4 of the time (during the week - the weekends were much busier) we had the whole bus to ourselves. Even the wait was pleasant... they have benches for you to sit on, and it's in a cool, shaded area.
Don't let the transportation keep you from staying at the AKL. It's beautiful there, and I would stay there again in a heartbeat.