I have Fed 15 now. Because I have problems with Gnome 3, especially when using another screen ie 2 screens, I also downloaded xfce. I just booted into xfce, and I have no touchpad scrolling, nor anything under Preferences>Mouse to enable touchpad scrolling.
I presume I need to download something. But what? In Gnome the scrolling works fine, at least it did earlier today! I have a synaptics touchpad, and I really like the scrolling, although I always have the 'tap to click' disabled, because I am always clicking by mistake when typing.