The fact that the framebuffer size is not the same as display resolution is known only to the driver and it is not something that is requested to be implemented for Linux.
Well whatever the case might be, whether it's kernel's fault, GNOME's fault, Wayland's fault or device driver fault, fact of matter is that one can easily get 1920x1200 resolution on Retina Macbook 15" with sharp font and images, and cannot on Fedora. This is why perhaps people are making "a fuss".
OS X CAN do fractional scaling as far as user is concerned (doesn't matter who scales it up or down), while Fedora cannot (with Wayland, at least).
It doesn't matter whether they know it or not, since they work transparently great with the scaling factor. In fact it's even better than having the software stack aware of it (simpler, less room for errors).
The end result is that fractional scaling resolutions works on OS X and not on Wayland (from what I read, haven't checked Wayland myself recently).