Apple does studies for these things. They studied multi-button mice and found it slowed people down. The reason is that they clicked on the wrong button some percentage of the time.
What throws people off is, when you make a mistake with a gui, you correct it and forget about it. You don't account for your time because your mind is focused on the task. But and independant observer, who observes you doing the same task in both situations will have a stopwatch and recognize objectively which takes longer.
In some cases-- such as people's preferences for keyboards over mousing-- they perceive that they are faster accomplishing tasks with the keyboard than the mouse. They think this because they press keys faster and the brain accounts for each key press as a bit of an accomplishment... but the stopwatch shows differently.
Its the same thing with the second button mouse.
Trackpads have changed the situation, as a more direct form of control, 2, 3 finger gestures take less cognition. And of course, millions of people prefer 2 button mice, and don't care if they lose a minute or two each day as a result.
So, while there is a reason for the choices Apple makes, those reasons can be less significant over time.
But my point was, there is always a reason, and you shouldn't try to cut new ground unless you understand the reason for the original method.