What about buying credence with a market sector?
I don't see many people ruminating about whether Apple may be putting more energy into going after the minority marketplace, and see Beats as a path to doing that. If Dre and Iovine can sell overpriced, not very good headphones to a TON of the "urban youth" segment, I think there's good reason to believe that Apple might think they can help boost other Apple sales into that market. That alone could be worth WELL more than $3 Billion. Demographic trends alone make this idea worth considering.
Think about it this way. Let's say Apple thinks they can sell $1000 worth of overall Apple products to 10,000,000 more people the Beats guys can "turn on" to Apple (and of course combine Beats' products with that). Apple's profit margins are what, around 37 percent give or take? I'm sure Beats' are in the same territory, if not significantly greater. That's $3.7 Billion in net profit right there. Can Doctor Dre hype $1000 in Apple/Beats products to 10,000,000 people? Or $500 in Apple/Beats products to 20,000,000 people? I think that's pretty reasonable, actually. In addition to this, Iovine and Dre's content business acumen could perhaps help Apple grow their content businesses (music, TV and movies, plus apps of course). This deal could actually be somewhat of a no-brainer for Apple, in this light.
Additionally, what I would HOPE to see is a refinement in the quality of Beats products, thanks to the resources of Apple behind the brand. If that happens, this could end up being a win-win-win. Out of left field yes, but maybe not as crazy as it looks at first glance...