It may have just been a matter of time, but it finally happened: streaming music is now the biggest cash cow for the American music industry. The RIAA's latest year-end sales report reveals that streaming accounted for 34.3 percent of US music revenue in 2015, barely edging past the 34 percent of downloads. Physical sales, meanwhile, were down to 28.8 percent. And despite concerns about free listening hurting the bottom line, paid subscriptions were the star of the show. While ad-based streaming pulled in 30.6 percent more cash versus 2014, paid subscriptions jumped 52.3 percent -- suddenly, forking over $10 a month for unlimited music wasn't such a far-fetched idea.