[bitteralmond]

A proprietary language created for a closed, for-profit platform isn't naturally the most popular choice for open source projects.

[mehrzad]

Noob question: is a language proprietary if its only compiler is proprietary or if the main one is? There are open source compilers for Objective-C.

[xymostech]

Considering that XCode uses a version of clang (which is open source) for it's compiling, I wouldn't say that the main compiler is proprietary either. I think that what people mean is that all of the "usefulness" of Objective-C comes from using it with OSX/iOS development, and all the stuff related to that is proprietary.