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.
A comment on this thread got me headed in the right direction of research. Before 1958, none of the bricks had tubes inside, though as gev points out, some of the larger bricks had horizontal cross beams. In 1958, Lego applied for a patent for a new design with center posts in the bricks, which allowed for a tighter more stable fit. So, the 1x2 brick without a post is likely a very old lego, and not a specialty piece of some sort. This was certainly not an effort to save plastic, but simply the idea of having a center post hadn't been created yet.