I think I know why now ...
My gut feeling is this behavior is deeply related to these 2 features on iTune:
- Synching with WiFi
- Startup iTune when iPhone is connected
Since I turned on , iTune began startup automatically by itself. It's almost foreseable that the iPhone is initiating the Synching with WiFi on some kind of schedule by itself. And, since  is turned ON, the initiating of  is causing iTune to startup on the desktop.
Obviously, I can turn OFF  but then, iTune will not startup even when I connect my iPhone physically to the desktop. I guess I can start up iTune manually.