Wait, what? If you work at Apple, you are absolutely prohibited from having outside projects, even open source projects that are explicitly not a part of your job?
That's so surprising to me that it feels like it can't possibly be true. The best hackers all have some kind of open source projects, and Apple feels very supportive of open source work. How could they attract the best talent unless they were fine with people building open source projects?
Apple is quite supportive of Open Source in an official capacity. I would actually say that the best talent almost certainly does not work on Open Source projects in their spare time (though quite a few talented people do get paid to work on Open Source projects). The "best talent" tends to have other hobbies outside of coding -- well-rounded individuals make better team members, especially when working with non-technical team members. A lot of young engineers don't appreciate this until they're older.
For me (even if they would offer me a job, which they probably would not) the second worst would be the extreme secrecy and the worst would be the absolute prohibition of outside projects, even open source unless it were explicitly my job.