When Apple was designing Mac as personal computer for everyone, a single button mouse is truly godzillion times better than two button. There used to be an Apple guideline on how to move a mouse and not to lift the mouse up into the air, but mapping the horizontal plane of the mouse to the vertical plane on the screen. Even that was difficult for some people.

People just dont realise how normal people have problem with mouse. Of course as we progress I think Two Button mouse could make sense as default. The role of PC also changed. The PC for everyone is now an Smartphone.