libsdl-ttf2.0 is from the Nokia repositories, libsdl-ttf2.0-0 is from Extras-devel.

libsdl-ttf2.0-0 <= 2.0.9-1maemo2 contains the same library as libsdl-ttf2.0 - they can't be installed at the same time.

libsdl-ttf2.0-0 >= 2.0.9-1maemo3 is just an empty package that depends on libsdl-ttf2.0

Now if you installed a game that depends on libsdl-ttf2.0-0 (and have 2.0.9-1maemo2 installed), you can't install a game that depends on libsdl-ttf2.0 later, because those two packages conflict.
You can't just update from libsdl-ttf2.0-0 2.0.9-1maemo2 to 2.0.9-1maemo3 either, because the latter depends on libsdl-ttf2.0, which can't be installed as long as libsdl-ttf2.0-0 2.0.9-1maemo2 is still there.
Now after force-deinstalling libsdl-ttf2.0-0 2.0.9-1maemo2, apt-get -f install can install the libsdl-ttf2.0 + libsdl-ttf2.0-0 2.0.9-1maemo3 combination to make both games depending on libsdl-ttf2.0 and games depending on libsdl-ttf2.0-0 happy.