Normal channels broadcast in 576i.
here is a list in what format the HD channels are broadcasting:
as you can see, most populair HD channels use 1080i.
The problem is, that you can only choose ONE particular setting, for every channel. The cisco will NEVER adjust it automatically to the source signal. The advantage of this is, that the cisco will never suddenly change to a signal that your TV doesn't support. But a disadvantage is that if you claim your scaler of your TV is better, you have to manually change the output format of the cisco every time you change to a channel with a different source signal.
I also favor an option to let the cisco just propagate the source format so you can fully benefit the scaler of your TV if you disire so.