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 [1], 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 [2] is turned ON, the initiating of [1] is causing iTune to startup on the desktop.
Obviously, I can turn OFF [2] but then, iTune will not startup even when I connect my iPhone physically to the desktop. I guess I can start up iTune manually.