For many hiDPI displays, the OS and the applications manage this. You pick a resolution in your display preferences to make everything look good (usually 50% off the native, that's what the OS will probably recommend). Lr and Ps detect this, and use this resolution for everything but the image itself, where they use displays native resolution. Many are not aware of this so they think they need to go to full native resolution to take advantage of all those pixels.
But I also am not sure if there are issues with the OS detecting the presence of a hiDPI display with some 4K monitors. It's pretty easy to test, set up your display for a comfortable working resolution in the OS preferences (try 50% of the native, this will appear the "sharpest). Open a small jpeg (around 1200 pixels) in Photoshop and view it at 100%. If everything is working correctly it should look considerably smaller than you are expecting. To see it at "normal" size you have to zoom to 200%.