¹ Actually, there are as many as you care to implement. These three are simply conventional; applications are free to use other names to identify other communication channels.
We're barely getting to the point where most people understand what you mean when you say "Copy and Paste that sentence" or "Right-click and select Save As".
Most popular software is going to be catering to the LCD for a long-time.
https://www.x.org/releases/X11R7.6/doc/xorg-docs/specs/ICCCM...
Note the copyright dates on that document.
¹ Actually, there are as many as you care to implement. These three are simply conventional; applications are free to use other names to identify other communication channels.