Transmedia + Storyuniverse

First of all, not every story/property needs to be or deserves to be or should be made a transmedia property. Many—many!—stories are perfectly fine as traditional, mono-media properties, and are in fact better. While John Green’s The Fault in Our Stars has spawned tons of fan art and creations, I would never want it to be a transmedia property—I think it would ultimately take away from the experience of the main part, the novel....
What you’re asking is actually a couple different questions: You want to explain to someone the value of transmedia, and you want to know if a traditional writer actually needs to do anything different when writing for transmedia.