I really wonder what you mean by UPSERTS. Because the traditional meaning for UPSERT is "UPDATE if exists, INSERT otherwise", aka MERGE. And you're right PostgreSQL is missing that, but hopefully we'll get something like that in PostgreSQL 9.5 at the end of 2015. There are ways to do that in PostgreSQL using writable CTEs, in some cases.

But that's completely unrelated to JSONB, so maybe you mean something else?

Nitpick: it's JSONB, not JSOB.