EDIT: To phrase it more bluntly:
"The only game to ever become a lasting cultural phenomena via internet virality is Minecraft."
... is mistaken. Mario is the most obvious counterexample, but there are dozens of others.
Dota became a cultural phenomenon, and has stayed a cultural phenomenon, solely through the internet. No internet, no dota.
It's simply mistaken.
Or do I need to prove Dota is a cultural phenomenon? https://www.youtube.com/watch?v=0OzWIFX8M-Y
I would say that franchising/sequels reflect the fact that if you have content which is just barely sub-viral you can pump money into marketing to get virality to get more money. Basically a controlled fission reaction instead of an explosion.