and if you want to go further you can right click on quicktime -> show package contents. then contents -> rescources. in there there are .icns files. these are the icons that this program assigns to all the files that are assosciated with it.
personally, i really dislike vlc's icon(s). so i found the generic movie icon, .avi, .mpg icons from quicktime and put them in vlc and also swapped the vlc cone icon to the quicktime Q.