When something on a mac looks like it should be able to be frobbed, dragged, etc., it usually can and in exactly the way that it seems like it should.
This is not the case on Windows, Linux, or anything else.
1. It's way the hell better than Windows. No competition here. Windows is horribly clunky, and if you disagree with me, try using both for a while.
2. It has less of a tendency to plunge you into pesky little technical details than Linux. I personally don't mind fiddling with a config file every now and then, and the more recent Ubuntu versions are getting surprisingly good about this, but Linux still demands more effort to get a good, productive environment going. And Flash support still sucks.
Of the two, I prefer Linux in terms of usability. I doubt most non-technical users would agree. (Chrome, though, is just unambiguously better than Safari in every way. I use both regularly and don't want to dislike either of them.)
The same caries over to other things. Sure the install and uninstall of applications on OSX is a great UI. But apt-get just seriously leaves it in the dust. The problem with linux was never that it had a bad UI or was too customizable. The problem with linux was actual hardware bugs in drivers, lack of office, lack of flash, lack of games. Which have mostly been addressed asides from games (which is a sore point for Apple too). UI is far too overrated over actual features.
And it's all based on a myth. Steve Jobs ringing up SUN over their looking glass and threatening with UI patents is just ridiculous. As are the claims to Apple fame with interfaces taken from Xerox.
So yes, I agree Apple are very good, possibly the best at UIs. But my points are 1) UIs aren't as massively important as people say, 2) Apple's "innovations" have been overrated 3) your statement that "no human beings on the entire planet other than those that work at One Infinite Loop in Cupertino are capable of doing a UI" is just ridiculous.