In reply to Macbook Pro, retina screens, hinting, the future:
Well, you wouldn't be the first to question some of the terminology adopted by the W3C for their CSS specifications. ;)
Té's 96ppi comment *is* related to the spec. The W3C refers to a 'reference pixel' in the latest working draft:
http://www.w3.org/TR/css3-values/
"Note that this definition of the pixel unit and the physical units differs from previous versions of CSS. In particular, in previous versions of CSS the pixel unit and the physical units were not related by a fixed ratio: the physical units were always tied to their physical measurements while the pixel unit would vary to most closely match the reference pixel. (This change was made because too much existing content relies on the assumption of 96dpi, and breaking that assumption breaks the content.) "
Granted, it's still up to browsers to decide what to do and not all care. For instance, there are several high-density BlackBerry devices where the pixels are simply smaller. Which is unlike the iOS reitina implementation where the 'real' pixels are much smaller, but the 'virtual' pixels remain the same offering a more predictable rendering in terms of physical size.
At some point the operating systems/OSes will have to just do away with the concept of pixels altogether (at least from the perspective of the content authors). As we approach much higher density screens, adopting a resolution independent system would make more sense. That way 1" = 1" regardless of the particular screen. Fingers crossed.