Streams is like the radio. It costs anywhere from 80 cents to $1.50 to download a song, where often streaming is free, or really, really cheap (iTunes radio is free, Pandora costs what $9/month - for how many songs?). If Apple is paying per stream but not charging for it, they're doing the artists a favor.
As the article states the first three months (trial period) is free after you will pay 9.95 a month IIRC.