It seems that if you enable Standby and have Preloader ignore the settings, you can power-down fine from the System menu, but not if you try to do so from the Homebrew Channel (actually goes to Standby). Perhaps that this is an issue with HBC's shutdown code, or it can be worked out from Preloader's angle, I don't know. Guess I will either not be using Standby (I never use News/Weather), or not be shutting down from the HBC.