The AC power management options are exteremely limited.  Being plugged into an AC outlet does not mean that I want to run my laptop hot, at full power, with the fan blowing, and the CPU using as much juice as possible.  My AC outlet may be a power inverter connected to a deep cycle battery.  I might live somewhere where electricity is very expensive.  I might have a lot of devices whose AC power profiles I need to minimize, not just one computer.  My house wiring might be subject to brownouts if I have too much of an electrical load.