While I do think think they're gradually dragging OS X into a very iOS-like future, it seems like a stretch to link sandboxing to their desire for control over our mp3s.
MP3? That's myopic - and I never talked about keeping Hollywood and the RIAA happy.
No, this is about a highway tax - to get recurring revenue in business-speak - and sandboxing will ultimately help prevent jailbreaking and unlocking, which lets you load content as you please.
Just look at where they make their money! Software companies are valued based on how well they get customers hooked on subscription type payments. Apple is building a delivery channel - and wants no alternatives.
Look at the product direction - no detachable storage for the iPhone, iPad - no blu-ray optical media for the bigger siblings - and with Thunderbolt, do you think the MacPro will have an optical drive in the next rev? I see convergence btw the MBA and the Pro in two years or less.
Looks pretty clear to me, the goal with their Cloud, iTunes, sandboxing etc activities is to prevent users from going outside their format. In many ways that is aligned with client needs - it is easy, it gets backed up, always available... but you
will pay for your "subscription"