I don't know, if this Retina 15" was calibrated or not - it's a new one in an apple store.
But if calibrated or not, i found out, that 4 different high resolution screens have a lack of dark grey presentation (even my ThinkPad T440s FHD IPS, which is definetely calibrated with a Spyder4Elite).
My personal resumption: people need to take care before buying a high resolution display (even when it's calibrated). Eizo professional photographer screens don't have (and need) high resolutions, because each pixel is a native one. It's just a question of panel quality.
Many people like to have Retina, because of the extrem sharp and colourful display. But they often forget, that such a panel is not even the first choice, if working with greyscales is requested.