Support (of what I consider to be the vastly superior) the "select / paste-current-selection" method is inconsistent (that's me being polite) on modern desktops. I'm now no longer sure what I'm going to get when I hit paste, sometimes the right thing, sometimes nothing, sometimes something from a week ago.
Ctrl + c was always used to send a SIGINT to a program, I always thought it odd when window managers started copying windows keyboard shortcuts.
I'm now trying to remember how we did handle copy/paste back in the days of twm/fvwm/olvwm, I seem to recall a whole bunch of clipboards that never kept in sync. The History of Copy and Paste - there's a book title for you, granted it probably won't be a best seller.