Apple has become something of a fashion brand. While they still make some very good technology clearly many people buy their products for other qualities. Perhaps Apple think they risk being seen as an old persons brand and young people might defect to the competition. Buying Beats seems like a way to try and buy credibility amongst a new generation. Given that many tech buyers are fairly ignorant pushing branding and celebrity endorsements probably isn't a bad way to go for shareholders. I might think Beats is rubbish but I think most things teenagers like are rubbish so I would never make money out of them.
If they start selling MacBook Pros by Dre with loud colours, crap specs, celebrity endorsements and even higher margins than currently I think Apple will have lost the plot.