It's something else on your computer that requires Itunes... but virtually impossible to say what because there are loads..
It could be a desktop widget, a music program that runs in the background, so have a think about what you may still have running that might require itunes for anything,
iTunes "does its own thing" regardless of whether it is the only thing that I have open or if I have multiple programs open. Having said that, I don't use a multitude of "media-type" programms - all I'm usually running concurrently are Hotmail, MS Word, MS Excel and Internet Explorer.