> Why are you choosing Cassandra every time?

Linear horizontal scaling (double capacity? double # of nodes), no SPOF, Active/Active/Active cross-WAN HA.

> And what's your refutation for his desire to use MySQL over some other database, from his point of view as presented in the article (e.g. availability of support via Google/SO)?

Hire people that can learn DB internals and be the expert you want to see in the world: http://stackoverflow.com/search?q=user:4774369+[cassandra]