Should we talk about people who use three button mice? In the days before scroll wheels such mice existed --- I have one in my junk box. :) How about five button mice? Seven? When does "left" and "right" become meaningless? Should those terms be used at all?
Just to interject one comment, yes, people still use mice with three or more buttons. Usually the scroll wheel can be pressed down to select with the third mouse button, and gaming mice have even more buttons next to the primary and secondary buttons.
One of the strenths of TDE is the fact that all three buttons can be used to interact with an on-screen element, each having a separate function bound to it. This is one of the things that I miss most when using Gnome or a Macintosh system, and KDE4 had some of the same problems when I last tried it.
Tim