Quite. Things are not "easter eggs" if they are used by the overwhelming majority of users of that environment, and widely documented. Middle-click to paste is *not* an easter egg. Heck, it was the first thing I ever learned about X, before I even learned how to start an xterm!
It's culturally transmitted knowledge, sure. So is the do { ... } while(0) pattern for statement-like macros in C. Maybe we should remove that too?