You're conflating your desktop environment with your window manager. For example, I run xmonad on top of xfce and use the standard xfce tray, wifi config, etc. Xmonad just replaces the xfce window manager.
To be even more specific, network management is really distro- and DE-agnostic. For instance, Arch wiki describes a multitude of ways for wired [0] and wireless [1] network configuration, that would technically work in other distros as well.
Most distros and DEs ship with Gnome's NetworkManager [2] but with different front-ends: distros with GTK-based DEs like Gnome or Unity usually ship network-manager-applet, and distros with Qt-based DEs like KDE usually ship plasma-nm or networkmanager-qt.
Power management [3] is a bit different. There are distro-specific recommendations and also 3rd party apps, but DEs usually have their own power manager.
Now, when you choose to use a DE, the choice of which network or power management solution you use is already made for you, but when you don't use a DE then you will be choosing them yourself.
[0]: https://wiki.archlinux.org/index.php/Network_configuration [1]: https://wiki.archlinux.org/index.php/Wireless_network_config...
[2]: https://wiki.archlinux.org/index.php/NetworkManager [3]: https://wiki.archlinux.org/index.php/Power_management