Success for Apple Music makes a good headline—and goes some length toward justifying the $3 billion Apple spent to acquire Beats last year. But the actual business impact is small. At a starting price of $9.99 a month, the paying-subscriber figure amounts to at least $65 million in revenue—or about 0.3% of the $20 billion in total iTunes service revenue Apple is expected to report for its fiscal year ended Sept. 27.