While I mostly agree with the general point you're making, please do not confuse one particular kind of heavy work with the much more general "real serious use".

Random case in point NASA is using pgsql for handling data streams from several of their probes, is that not real serious use ?

I was thinking of something like NASA vs Farmville. Two left joins doesn't make a strong database case.

If you're willing to throw mapreduce at everything as a solution, you won't need Oracle nor will you know how to take advantage.