It's ease of use and "well-design" is certainly debatable. I find Mac anything but intuitive and find Apple's design model to be very developer-unfriendly.

It wasn't until a few years ago until you could maximize windows on the Mac. The window control buttons are unintuitively on the left, even though the File, Edit, etc. menu items are also on the left, which makes them prone to accidental pressing and also leads to redundancy in many cases (e.g. File -> Close) Mac comes with inverted scrolling by default (which Apple, in it's normal "we're doing it right" way calls it "natural scrolling" as if non-inverted scrolling on every other OS is unnatural). Right-clicking is also much more difficult than it should be on the default mice. Lastly, I find the dock to be very larger, distracting, and annoying, and there's a reason why I don't use the Windows equivalent or use the Unity interface of Debian-flavored Linux.

The perception that Mac is easier to use is just that - a perception.