ttmkfdir sometimes doesn't generate strings for fonts. For example, the fonts in /usr/share/enlightenment/E-docs (from the enlightenment package) are not recognized by ttmkfdir. Some fonts are recognized. The ttmkfdir at http://www.darmstadt.gmd.de/~pommnitz/ttmkfdir.tar.gz does create entries for these fonts, and in general more than the freetype package's version. PS - freetype was not listed as a category.
this has been fixed for the next release.