Don’t know what to tell you, then. It seems to work for me. To double-check, I just set the Energy Saver options on mine as follows:
“Put the computer to sleep when it is inactive for:” (Slider set to 10 minutes).
“Put the display to sleep when the computer is inactive for:” (Slider set to 10 minutes).
“Put the hard disk(s) to sleep when possible” (checked).
Wake Options: Both checked
“Automatically reduce the brightness of the display before display sleep” (unchecked)
“Restart automatically after a power failure” (unchecked)
“Show battery status in the menu bar” (checked)
Processor Performance: “Highest”
I closed the Energy Saver panel, and waited. The screen did not dim at all. It went straight from bright to off when the iBook went to sleep ten minutes later.