There are people out there who hate mice. There are even people out there who are physically incapable of using a mouse.
I can see that a specialist distro focussing on, say, a community of artists, might reasonably make a mouse a requirement. I cannot see why any general purpose distro should lock out a mouseless user. If this is the intention of Xfce then it seems Ubuntu made a very poor choice and should have gone with some other desktop. Otherwise it's "humanity to others, except others who don't use a mouse!".
Sorry, I'm drifting off topic. Inspiring photos of an inspiring install -- a great thread to direct people to when they say "I've got this old machine, I'm thinking of throwing it away!". Thanks!