From my experience with iceBooks they keep the USB ports powered all the time.
I used to have this USB Light and even when I would put the iBook to sleep (naturally expecting it to power down the light as well) ... the light would still be on. So, in the end I just left it plugged into the iBook and used it as a night light
Further, if you have a Logitech/M$ Optical mice and move them while the iBook is asleep ... that will wake the iBook (only briefly is the screen is closed). I have not been able to repeat that on my TiBook ... where wake from sleep only happens if I actually disconnect the mice in question.
I am sure the whole "Turn Off" deal is not a biggie. Plus with 10.2.4 being as buggy as reported I would not be surprised if things *work* differently from machine to machine. Personally, I am still on 10.2.1, but need to goto 10.2.3 because of a few issues I am having.