The problem with Ping was that you couldn't share music with people--unless they bought it and it didn't incorporate other social networks. Incorporating social sharing into a streaming service essentially gives users the ability to do that, provided that a large number of people actually use the service. However, if they limit sharing to iTunes accounts or Apple ID's--and exclude Facebook and Twitter, that's going to be a problem again. People need to be social where they're already social. Adding another network into the mix doesn't help.
I like that they're building a platform for artists, Jimmy Iovine alluded to that during one of his ReCode interviews. If artists can use the platform as a business tool, it will make streaming inherently more valuable. Hopefully they don't just limit this to major label artists though. It's the indie's that will benefit most from that level of interaction.
It's also likely considering Beats Music's acquisition of Topspin not long before the Apple buyout. Topspin lets artists build online stores that can be integrated into multiple platforms. They can sell vinyl, t-shirts, concert tickets...whatever.
This is absolutely key to making a streaming platform work for artists--which is really the key to making it work at all. Currently, what most streaming services pay out to content owners is ridiculously low. They're only going to wait for it to generate money for so long before they pull their content.
If an artist can generate revenue from streaming, interact with fans and have a storefront all within the same app--Apple could rule the industry again. Nobody else can build that, at least not quickly. Apple has the cash to offer more lucrative terms as well, if they wanted to get exclusive content that competitors can't offer. If they wanted to guarantee a penny per stream (double what most others pay) they could. They'd take a little bit of a hit initially, but would dominate in the long run.
Even if content is available through competitors, artists will steer fans to the platform that treats them best. This is an easy win for Apple, if they don't decide to screw it up.