I'm not sure this a fair analysis. Yes, Pokémon certainly added a nice built in fanbase, but I don't think that alone would have made it the social phenomenon it currently is.
As the article mentions, the gameplay is significantly easier than Ingress. Also, the theme is much more family friendly and less paranoid. It's got cute pocket monsters you can collect throughout the day. Additionally, the camera aspect makes it built-in social sharing material, especially since it's a palatable theme.
I'm not going to share Ingress photos with anyone else, but a humorous picture of Magickarp flopped on the beach is fun to share.
I'm seeing a lot of people who are completely ignorant of Pokémon playing this game. I see parents downloading it to go on walks with their kids. It's fun, easy, and fits in nicely with people's aspirations (more exercise).
None of that was really in place with any of the previous iterations. They were all too "serious", dark, and/or niche audience.
I suspected Niantic expected this to be a moderate hit with Ingress players and Pokémon fans - both were a niche audience. It's the gameplay and family-friendly theme that has made this as popular as it is.