"And the database world is moving towards scaling horizontally rather than vertically."

I think that's an oversimplification. Two counterpoints:

* Database systems will always need to make heavy use of locality. The speed of light means that synchronizing access over long distances (even medium distances -- light only goes about a foot per nanosecond) will always be a challenge.

* Multi-core means vertical scaling is back in (if by "vertical scaling" you mean "scaling on one box"), and probably for a while.

Postgres is doing an excellent job at both.

I do agree with the less-exaggerated point that postgres really needs to improve its multi-machine scaling. But it's far from a solved problem on any system under discussion.