The "2x" describes the image, not a property of the device that image is being viewed on.
If I have an image meant to be displayed in a 250x250 area of layout, a 500x500 "retina-ready" image will not fit. The browser must be told that the image is meant to be displayed "@2x" (as Apple puts it). This is what the "2x" is for. The browser is allowed to use any or none of that information in its decision making.
The syntax of srcset="" was chosen to match CSS's image-set syntax. The <audio>/<video> pattern wasn't great for anyone.
If I have an image meant to be displayed in a 250x250 area of layout, a 500x500 "retina-ready" image will not fit. The browser must be told that the image is meant to be displayed "@2x" (as Apple puts it). This is what the "2x" is for. The browser is allowed to use any or none of that information in its decision making.
The syntax of srcset="" was chosen to match CSS's image-set syntax. The <audio>/<video> pattern wasn't great for anyone.