That completely contradicts the manual -- see the note at the bottom of page 77: "The value set at "Picture Adjust" is stored in the memory individually for each input source." (my emphasis added)
The way I read the doc it says that these settings are only available if one of the listed sources are selected. I did confirm this on my unit. With HD radio selected I do not have the option for video settings under "Audio/Video Adjust" however with a source that does have a video option these settings are available.
your test does not confirm/disconfirm whether the settings are memorized individually by input; all it confirms is that "Video Settings" are not available for an AUDIO input!! The note to which you refer is only saying that "Picture Adjust" settings are only available with one of of the VIDEO inputs, which makes total sense and is fairly self-evident.
The operating question is whether you can have DIFFERENT settings for contrast/brightness/color/etc. for your Blu-Ray player versus your cable box versus your Wii or whatever.
What you need to test is this:
1. go to any of your video inputs, go to Picture Adjust and change something, e.g. set "Contrast" to "+3"
2. switch to a DIFFERENT video input, go to Picture Adjust and then see if the change has carried to the other input; if Contrast is still on the default "0" you know it's independent by input.