Can only mac people answer the thread maybe, to many seem to be confused with the App Store for iOS devices. The Mac App Store was released very recent and is aimed at desktop computers.
Some of the benefits would be
a) huge massive PR value and exposure to almost every single Mac user. I can’t image getting this kind of exposure for (almost free) anywhere else. I would download blender from the Mac App Store and rate it 5* just to help it become the #1 downloaded free app.
b) Practical, Code-Level Technical Support Tailored to Your Development Needs
When you request Technical Support, you’ll be assigned an engineer with subject matter expertise for your specific issue that can help you troubleshoot your code
c) Mac Developer Program members can access a range of pre-release Mac software, including Mac OS X, Mac OS X Server, development tools, SDKs, and more.
but maybe the blender foundation is already enrolled as mac developer program, if so every mac developer could get the membership and gain access to pre-release Mac OSX. Which would be beneficial also.
I have a hard time see apple want OSS to be destroyed since they host some of their projects as OSS (GCD comes to mind straight of) and I know apps being developed with OpenFrameworks C++ lib for iPhone before.
Anyways it would be a way into a platform known for lacking 3d suites …