Same here. At first I thought that WidgetLocker was allowing this in 4.0.4, as it never did this on 4.0.2. (WidgetLocker has this option).
But, when I unchecked the option in WidgetLocker to wake with hardware buttons, pressing volume up or down still wakes the GNex.
So, I would conclude that 4.0.4 has this "feature" built in.