Postgres is poisoned

Postgres is poisoned, as it is released under a BSD licence. This licence, dating as it does from an earlier time, does not oblige vendors to make their modified versions Open Source. Thus, IBM (or anyone) could alter Postgres subtly but incompatibly, cage up the Source Code and lock you in.

It's not called the "Bait, Switch, Destroy" licence for nothing.

At least the MySQL codebase is under the GPL, so it could always be taken over by someone else if Oracle seem to be neglecting their duties.