In the beginning the mouse was a Mac mouse, and it was good, or at least good enough. With Windows, the PC got mouse, and to be different from the Mac, the PC mouse had two buttons. But no one did much of anything with the second (right) button.
With Windows95, Microsoft implemented some cool right-click functionality and only then did Mac users start to say “Hey, how come WE don’t have that?”
Backwards compatibility with existing equipment has demanded that the MacOS not require a second mouse button to do second mouse button things, so Apple implemented second-mouse-button things by using Control-click.
Soon, though, with MacOS X, the Mac world will move to a multi-button-mouse default assumption.
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