So you're in the middle of busting a move to the transcendental heights of The Macarena; and what happens? The Roving DJ changes the BPM and your song cuts to Achey Breaky Heart! Sounds terrible.
Patenting the world? That's ridiculous. What Apple is doing here is patenting a specific method for real-time data sharing and collaboration through a trusted moderator. The "silent disco" example of applying this method is just one, and likely a trivial, potential application for this technology. I can easily imagine gaming and business uses for this type of communication mechanism.
So you're in the middle of busting a move to the transcendental heights of The Macarena; and what happens? The Roving DJ changes the BPM and your song cuts to Achey Breaky Heart! Sounds terrible.