XFCE itself is still written to be modular and lightweight (although the definition of lightweight has changed over the years). Most of its components can be installed separately with few dependencies. Distributions like Xubuntu and Fedora pile on tons of packages to fill up the CD images and present a nice, full-featured desktop to new users. After the Gnome3/Unity upgrades I switched to Xubuntu and just rip out about 50% of the packages after doing a clean install.