The title of the post is very misleading: Obj-C would crash and burn if there were native, supported alternatives in OSX, it survives exactly because there are no alternatives.
The same is possible on iOS as well, with the (significant) condition that Apple must first explicitly approve your use of a non-Objective-C runtime before your app can be posted to the App Store.
But in direct response to your post, Obj-C has a rather level playing field on OS X and still survives vs. the alternatives.
* it's not officially supported by Apple
* it binds to Cocoa (and if you're lucky it's even up to date and doesn't have that many bugs)
* you can't use it on iOS
* you can't get a job doing X instead of Obj-C because almost everyone just uses Obj-C, the Apple supported language
MacRuby is an Apple project.
PyObjC isn't, but ships in Mac OS X. That's rather officially supported.
> * it binds to Cocoa (and if you're lucky it's even up to date and doesn't have that many bugs)
Not true. MacRuby is a prime example of a language that taps directly into the Objective-C runtime, eliminating the need for a bridge. And PyObjC is a great example of a mature bridge – it's been around and robust since the NeXT era.
> * you can't use it on iOS
http://mobileorchard.com/announcing-iphone-wax-native-uikit-...
> * you can't get a job doing X instead of Obj-C because almost everyone just uses Obj-C, the Apple supported language
You can't get jobs programming Ruby, Python, C#, Lua or any other language?