actually I think they do adjust if you are up or downhill, or over a bump. I have seen the beam from my headlight just jump up or down when I am on a bump or on a slope. I still like watching the headlight adjust itself, especially when you first start the car (the most obvious time), even after 3+ month of ownership.
BTW, after driving the IS at night and then drive my dad's 99 RX w/o HID, the headlight of RX just seem like it is turned off. Never realize how big of a difference HID makes compare to normal head lights.