That platforms win by consumer preference is a truism that need not be underlined. Android benefited from homogenization by the OHA consortium, and its licensing permitting extensive reproduction by off-the-shelf producers of varying production quality. iOS benefited from Apple's branding and cult following.
What's relevant is that most consumers do not evaluate software platforms from technical and system properties. They seek mobile devices for their end use, and will inevitably steer towards what already has large units stocked, what is advertised and what is recommended via word-of-mouth which will usually create reinforcing loops from consumer impressions caused by the former two. That is to say, the mobile OSes are substitutable goods. Which mobile OS prevails is of little relevance to most consumers, who seek means to ends and the nature of software is that the precise workings of these means are often obscure to them or otherwise not important provided ends (telephony, messaging, browsing, productivity apps, entertainment, or communication and consumption in general, etc.) are met.
For there were other platforms besides Android and iOS, and those would have evolved just the same and we would be speaking of some other location exerting cultural dominance. If it weren't Google, it could have been Altavista or something else. If it weren't Facebook, it could have been MySpace, Friendster or something else. Especially social networks are by definition something that critically depend on Metcalfe's law. Mobile platforms as well, to an extent (largely because apps that people want will converge to them). People do not care that they use Facebook or iOS, they want access to networks of contacts and to communicate with them through a consistent mechanism.
As such, you cannot argue that SV culture has dominated just by the fact of some product being influential alone, since it's a circular argument that ignores most such technologies are not pursued for the actual technological properties.