A quick word about the half bottle: While large-format bottlings are coveted by collectors for their ability to stand the test of time, the half-bottle is doted on by and loved all the more for its ability to zip into the future ahead of us - delivering the pleasures of tomorrow, today.
The chemistry (or is it physics?) here is pretty simple; a similar amount of air trapped in the bottle with roughly half the amount of liquid, thus the air to wine ratio is much more severe. That said, this format also offers the perfect amount of wine for the quiet evening, doling out about 2 and a half glasses.
With all this acclaim, why don't you see more half bottles of great wines? The answers are simple: the glass for halves is more expensive, the bottle requires a smaller label (read: increased printing costs), and in some cases different bottling machinery.