It's not really an announcement for a developer conference. Plus aren't these things typically announced after the markets close (which wouldn't be possible at WWDC)?

Eh, Apple is Apple. They announced iTunes Radio at WWDC 2013, and that doesn't have an API or anything for developers.

And I'm not sure about announcing acquisitions outside of market hours. Apple does plenty of acquisitions that they never announce. Beats would probably need to announce being acquired if they were a public company, but they aren't.

Someone posted a video of Dre drunk at a party confirming the deal. I'm guessing Apple is in damage control mode at this point and would have liked to announced it later.