[breser]

As far as I know the LLVM tools (and it's not just clang there are others as well like clang-analyzer and lldb) that come with XCode are just binaries of the open source project. If there are any differences I haven't noticed them and I've built and used LLVM tools from source builds as well as Apple's binaries.

Since Apple has so much influence over the project they can simply get the changes they want into the project so that diminishes their need for their own changes.

The things they want to hold back almost entirely go into XCode's IDE. For instance XCode's IDE has a very nice visualization for the clang-analyzer. The visualization is just using the output from the open source analyzer. You can even replace the clang-analyzer with a newer version and use it from XCode. By keeping the visualization implementation in XCode itself they can maintain an advantage for their platform.

I'd say that this just proves his point since Apple has chosen not to produce a proprietary compiler and instead to contribute to LLVM.