I've worked on both Mac and Windows for awhile. However, I'm still having a hard time understanding why programmers enthusiastically choose Mac OS X over Windows and Linux?

I know that there are programmers who prefer Windows and Linux, but I'm asking the programmers who would just use Mac OS X and nothing else, because they think Mac OS X is the greatest fit for programmers.

Some might argue that Mac OS X got the beautiful UI and is nix based, but Linux can do that. Although Windows is not nix based, you can pretty much develop on any platform or language, except Cocoa/Objective-C.

Is it the softwares that offer only on Mac OS X? Does that really worth using Mac?
Is it to develop iPhone apps?
Is it because you need to buy new Windows every 2 years (less backwards compatible)?

I understand why people, who are working in multimedia/entertainment industry, would use Mac OS X; however, I don't have strong merits of Mac OS X over Windows. If you develop daily on Mac and prefer Mac over anything else, can you give me a merit that Mac has over Windows/Linux? Maybe something you can do on Mac that cannot be done in Windows/Linux with the same level of ease?

I'm not trying to do another Mac vs. Windows here. I tried to find things that I do on Mac that cannot be done on Windows with the same level of ease, but I couldn't. So, I'm asking for some help.