Opaque bricks with no center post? What is the purpose of 1x2 red bricks without a post inside the brick? I know they often leave out the middle post on transparent bricks to make them look more window-like, but what about in opaque pieces? I have a few from bricks of this type that are probably from sets from the 70s/80s but I'm not sure what sets they came from, let alone what clever things you can do with them that you can't do with a regular brick of the same size.
I'd wager it was mostly to save plastic. Many of the 1x family of bricks used to come with far fewer posts inside, like so: http://www.bricklink.com/catalogItem.asp?P=crssprt02 but notice they quit making that style in 1969.