Sure there are ways to Apple amass a large user base with Ping, but I think it is hard to fight with the extensible, and relatively open, Facebook that can be accessed from any browser, I see no point for someone that does not use iTunes Store, an iOS device or iTunes installing iTunes only to use Ping.

I think that initially Apple does want to use it to profit more with areas that they already are strong and also gather some experience running a social network, and them expanding it, maybe with user media sharing and an API. I think games and apps will be a next focus areas for Ping.

Of course it'd be a hard fight. But that it'd be a fight at all makes them 1000x more dangerous than anything else in the last few years.