Now for XFCE, their programs have a different goal in mind: light weight. They remake programs and make sure that they don't have unnecessary bloat. Since their design decisions come from GNOME, they use GTK for this. That results in another separation when it comes to Razor-qt: their desktop is Qt, but loading the KDE libraries is super slow, so they also want their own light-weight Qt apps.
Besides that, I don't think anyone else is making specific programs. LXDE and XFCE share the programs to some extent. The WMs, like Fluxbox, don't trouble themselves with programs to begin with. Enlightenment is doing something, but I never used E17 so I can't really comment on that (although I hear good things about it).