Bravia Sync only works with up-to-date HDMI devices. It is not so easy to make things as clever as you'd like it, when dealing with older legacy inputs. HDMI is easier, since the DVD when turned on can just basically tell other side "hey, turn on & switch to this input now, wherever I'm connected", using std agreed upon protocols by all the major manufacturers. Can't do that with composite/component since there's no intelligence on the input, it's just an analog voltage representing a video signal. Instead you'd have to add protocols for the TV to tell the receiver what legacy inputs it had, and add UI for the user to tell the receiver which input on the TV to use for each analog connection. It could be done in theory, but they were aiming for something very simple for people who only used new components with HDMI, not something that required complicated setup. Also it's HDMI-CEC so supposed to be compatible with other brands, which explains its simplicity even though they'll only claim working with other Sony Bravia.
You shouldn't have to switch the feature on/off. Just have to hit the right input button on the TV when you switch to analog. The Harmony remote is the better solution for all this anyway, works with any type of input, any mix of brands of components, any old component. With Harmony can turn this feature off completely.
