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It's a bit unfair to the KDE developers to say they rely on Trolltech for all their documentation.
The KDE developers provide a significant amount of documentation themselves using Doxygen (see http://developer.kde.org/documentation/library/3.4-api/). Further, there is a good collection of tutorials, HOWTOs and even a book on http://developer.kde.org. Finally, there is a good doc bundle supplied with KDevelop, which includes a tutorial on developing a basic KDE application. With the exception of the books (free online copies of a KDE 2.0 book [now a bit outdated], a Qt3 book and a C++ book), all of this was developed by KDE volunteers.
KDE adds quite a bit of added value to Qt. If it wasn't for the quality documentation, a lot of that wouldn't get used.