While I'm sure most people here have many documents open at once, I really wish I could show you the type of users who ask "where did my documents go?" when they have more than one window open and the first window is hidden obscured by the second.
No need, I think we all have family members who have asked this exact question. ;-)
I'm sorry but I really think this is a non-argument from an accessibility and usability POV. This is almost assuming the user is too stupid to learn how a specific application works. Anybody can be taught, and anybody who is able to use Inkscape should be able to use it.
The analogy with MS Word is wrong as Word is a totally different kind of application and targets different user bases. No to mention Word isn't exactly the greatest example of UI usability (pre MSO2007).
IMO it is much less convenient to allow a non-controlled taskbar to handle the arrangement of documents rather than managing them from within the program itself.