When you think about it. This attitude towards employees is just a reflection of company culture, let me explain.
Everyone talks about how the App Store is a "walled garden" but when you step back, all of Apple is a "walled garden" in a sense. Apple is in many ways like Disney when you think about it, they are masters of their respective domains, they have intense attention to detail, and they attempt to control and curate the experience for you. This is not necessarily a bad thing in all respects, in fact it's a very good thing, the whole reason I go to Disneyland versus Bush Gardens is that I want that impeccable attention to detail. Likewise I have an iPhone and I bought it precisely because of the attention to detail and the consistent experience.
But while this need for control is a huge advantage in some ares, it's a huge disadvantage in other areas, namely the App Store. We have all heard the grievances with apps getting pulled and this again is reflective of the walled garden. Out house, our rules, no exceptions.
But it's really interesting to see this culture extend to the employees themselves. Apple not letting employees contribute to OSS is again very reflective of the "walled garden" approach. Everyone else's employees work during the day and do other stuff on the side, but Apple employees are 100% inside Apple.
And this is a real issue for Apple, because the thing that makes their hardware so good is the same thing that makes all their software less than ideal to work with, to put it mildly. I think the best indicator of this right now is WebKit and Safari. Chrome and Firefox are light years ahead of Safari in terms of implementing new web technologies. At it's core, this is a problem with the culture at Apple of letting people in, and until they fix that culture or make a concerted effort to improve it, any attempt at them trying OSS is going to fall flat.
Apple needs to focus on diversifying its leadership and bring in new ideas. They could learn a thing or two about API's and Software from a company like Stripe.