Wait... As for me kdm-3.5.13 parses desktop files located in the /usr/share/xsessions/ and displays KDE 4 session as "KDE plasma workspace". If r14 doesn't this is a regression.
TDM recognizes /usr/share/xsessions/ in R14 too. I recall I raised that issue and was part of the testing.
That said, the KDE4 session desktop files are not installed in /usr/share/xsessions/. They are installed in /usr/share/apps/kdm/sessions/, which is why TDM does not find the files. :)
Darrell