"the top face of the highest block that can be placed is at Y-coordinate 256." -http://minecraft.gamepedia.com/Altitude http://minecraft.gamepedia.com/Altitude

"the top face of the highest block that can be placed is at Y-coordinate 256." -http://minecraft.gamepedia.com/Altitude http://minecraft.gamepedia.com/Altitude I'm pretty sure what you're thinking about did happen: the height limit used to be 128 and when Notch added some code, it made for a (relatively) big improvement to 256.