This is a very good point, and I'm sure it depends on all 4 of things very heavily. There were multiple Facebook competitors, but Facebook executed their produ

This is a very good point, and I'm sure it depends on all 4 of things very heavily. There were multiple Facebook competitors, but Facebook executed their product MUCH better than everyone else (real names/people, exclusive to certain communities at first) and I would think it was a big cause for their success. As for Android, I was told recently that it was released in a time when carriers (Verizon) defined what apps should be shipped in phones, and largely commissioned manufacturers to make said apps.. Android helped make this a non-issue by letting anyone make apps, making a market, and letting every phone manufacturer ship it for free (no one else did this). Even if Android was crappy in comparison to the iPhone initially, it provided a lot of freedom for the manufacturers, making it very attractive. Not to mention every non-iOS/Android mobile OS back then was garbage in comparison.