Can you pastebin your xorg log file, just in case there are any relevent error messages ?
My guess is that you *are* getting power savings, just not as much (yet) as you would with a discrete GPU. The HD3200 is connected via HyperTransport rather than PCIE, and the drivers only have code for PCIE lane reduction, so I suspect they don't save as much power on an IGP as they do on a discrete GPU.
The current power management code is just "the low hanging fruit" - it's maybe 1/10th as complex as the code in fglrx. Once kernel modesetting is in place I expect more sophisticated power management code will follow right behine.
We also recently released programming docs for the 780 chipset, which will help withthe implementation of IGP-specific power management features.