I'm not trying to start a flame war here--it's an honest question--but why do you rank Linux below Windows? Why is Apple above them? I've never used a Mac, so I don't kow anything about them.
In initial out of the box usability by people who go in knowing functionally nothing about it, absolutely. The general test used for this stuff these days is connecting to the internet, right out of the box you can get an XP machine on the net in 10 or 15 minutes, Linux isn't there yet (not talking about how long it takes somebody who knows what they're doing before hand, we're talking about the green newbie) by a long shot, Apple's been there for a long time. Apple has been geared towards the complete newbie for a while, they were the first guys to color and shape code plugs (as far back as 93 at least the only way you could plug something into the wrong outlet on a Mac was with a hammer), they were the first guys to pretty much throw the final stage of configuration at the user in easy to understand wizards. Not that I'm a Machead (actually I don't really like them, still scarred from System 7) but really anybody who generally knows their way around computer logic can figure out Macs to the point of being a power user in minutes, they are really easy to learn.
It's all about the amount of effort put into HCI -- Human Computer Interaction.
Due to its nature, there was never a good central concerted effort to get a cohesive interface and general "way of doing things" in Linux for the average user. It's not quite out of its geek stage yet. And their best stuff just attempts to copy Windows.
Microsoft has spent the years basically just trying to copy Apple, and blown it for the most part due to the different metaphors, and thinking they can do it a bit differently and have it still work right.
With both Linux and Windows, usability guidelines for third-party developers aren't that good.
With the Mac, Apple has from day one worked on usability. They don't always get it perfect, but there is a general cohesiveness, with the computer trying to help rather than confuse you. They also have had for a long time very good and detailed guidelines for developers, down to what should go on dialog buttons (descriptive action language instead of yes and no) and how they should be placed, to the pixel.
As with Windows' Ctrl-Alt-Delete, the Mac's biggest former UI boo-boo (dragging a disk to the trash to eject) was only meant as an internal shortcut for developers. However, they've even solved that, as now the trash icon turns into an eject icon when you move a disk's icon.
Their biggest continuing (although getting better) boo-boo was copying the Windows Taskbar as the Dock in order to woo Windows users -- although they did implement it a lot better.