Personally, I don't have Windows 7. However, I have Vista and I can tell you that iTunes and Quicktime will not combine together in the taskbar. Generally it will only group items in the taskbar when there are too many items (saves space on taskbar). Also, it will only combine items that are very similar or are part of the same program (e.g. Explorer windows)
Here's another thought I had about this. Windows Media Player is designed so that you can hover over the icon in the taskbar, and it will open a small preview window that lets you control the music thats playing (replacement for the Mini Player used by iTunes and Windows Media Player in earlier versions of Windows). iTunes most likely does the same thing as WMP on Windows 7, which would explain why it's separating itself from Quicktime.
