> So the current existing version of photoshop can't access all the pixels then?
It can if you set the global resolution to 2880x1800, but because most UI elements are likely bitmapped it'll be unusable: a 30px button will remain 30px, but will be a quarter the physical surface.
Ah well, that would be sad. Though maybe not surprising either (after reading the article, it looks like the "emulated" resolutions are limited but games get access to the native resolution).
As a bitmap editor, it can access 100 times those pixels.
As a GUI, it renders as it always did in Retina resolution, i.e it is not shows it's buttons and labels any more detailed, or any smaller. This is how every non-Retina ready app behaves.
That doesn't affect how big an image it can edit at all.
It can if you set the global resolution to 2880x1800, but because most UI elements are likely bitmapped it'll be unusable: a 30px button will remain 30px, but will be a quarter the physical surface.