Maybe the long version is slightly more understandable: libfm-qt was in the beginning a wrapper around libfm. With the current release only a minor part of the libfm functionality is used, over time the dependencies to libfm was reduced and replaced by native c++ implementations. Second dependency from "old" LXDE is menucached.
With the 0.14 release series libfm-qt will be a pure c++ implementation that uses glib2 and Qt. The old dependencies to libfm are removed. Unfortunately this doesn't help much right now regarding libfm - pcmanfm-qt will still depend on menu-cached, menu-cached depend on libfm - so, bingo. But that isn't so bad as it sounds at a first view - libfm is small, menu-cached is small, our devs like glib (i can understand that) - so pcmanfm-qt combines the best things of both worlds. And menu-cached will only be loaded as long a user use the pcmanfm-qt application menu. This is the last part we use from LXDE directly. If one want to get rid of pcmanfm-qt - why not, just use some other Qt based filemanager, dolphin comes to mind. Hmm, wait, i guess that would not be a really lightweight replacement. To sum it up - libfm-qt and pcman-qt will not migrate away from glib2, dependencies to menu-cached and lifm will hopefully disappear within the next year.