After seeing study after study found that most people never right click it is hard to find one button stupid. I recall one KDE usability study I sat in on where some actions were only accessible via the right click menu. The user (who was a kde developer!) couldn't figure out how to complete all of the tasks because the actions were hidden and he happen to not right click on the "right spot" to see them. For the maintainer of the application it was an eye opening experience.

I completely disagree, but not for the reasons you might expect. Most people attribute Apple's decision to stubbornness, laziness, arrogance, vanity, or "just being different." It's not any of those, but Apple is so tight-lipped about their decision making that no one articulates why they make the choices they do. Their "one button" strategy is brilliant, and here's why:

As I said, the real reason Apple needs one button is to prevent interface designers from getting lazy. Apple (and their third-party developers) know that most people never change the defaults.

However, they don't really want to ship single-button hardware. Here's what most people don't realize: Apple knows it's a less expressive device. Back when they shipped real one button mice, their advanced users were forced to BYOHID. The hardware that Apple shipped was wasted. That sucks.

To resolve this dilemma Apple devised the Mighty Mouse (later the Magic Mouse). Since the "right-click" was in software they could keep the one-button default but have the hardware magically transform into a multi-button mouse for advanced users. Surely many will BYOHID anyway (this happens with PCs too), but two buttons satisfy many more users.

It's a neat solution to a technical and social problem.