Why do I see some of the software developed using cocos2d will judge is not iPad, and if so would set scale = 0.5, which is why?

Such as the title, set scale = 0.5 will not double the figure shrink it? Why high resolution iPad but need to narrow it?
Reply:
If we set to 0.5, the high-resolution screen that we have double the pixel density, so we will see each pixel.