Aren't Social Networking Platforms Supposed to be Social?

Let me begin by saying I am all for the advancement of social networking, web 2.0, and all the rest. In fact, I fervently support such advances that I find myelf writing about everything and everything to do with said topics on a frequent basis. But I think I missed or misunderstood something: shouldn't social media platforms inherently be open to as many users as possible, not limited by issues like users' choices in operating systems? On this lovely Sunday afternoon, I had every intention o