I double checked that behaviour with the Sourceforge version 2.3.2 of
NatTable. With this version the greater than matcher works.
In that version we had a custom ThresholdMatcherEditor that mostly was the
same than yours by fixing some bugs. As it was created before I joined the
NatTable team, I don't know much about it. With the move to Eclipse we had
to remove it (which is correct regarding intellectual property and updates
of GlazedLists). But this also means the greater than matcher isn't working
anymore. The user who reported this also checked that with a GlazedLists 1.9
and it seems to still exist.