I suppose this is a lack of maintainers?
Ultimately the answer would be Yes.
Xfce 4.6 is the current version in NetBSD. One of OpenBSD porters was, and I think still is, on the Xfce development team and had the huge task of working around the "linuxisms" that are finding their way into the latest Desktop environments.
Examples are the sound server: BSD uses sndio Xfce 4.6 used alsa or oss. Xfce 4.8 switched to gstreamer. Gnome has recently made pulseaudio a requirement. The OpenBSD developers had to "route" the output of these newer sound servers to sndio.
Other examples involve automounting devices in the respective filemangers (Thunar/Nautilus).
There is work ongoing to update the Xfce packages in NetBSD