This limitation is by design.
Taking into account the target hardware, factors might include, changing a wall paper might a low priority thing to do, since you are using your Netbook to surf the web, work in the browser majority of the time, email, IM, your desktop is most likely the last thing you are gonna focus on.
Why*can't I change* my desktop *background* ?
http://superuser.com/questions/69601/how-to-change-the-wallpaper-in-windows-7-starter-edition .
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