I think there was a window of time where this was not true and the majority (user-wise) of the Linux desktop was really strong, united, and standardized. This lasted approximately from the mid-2000s until GNOME 3 and Unity.
- Ubuntu had a polished GNOME 2 desktop.
- Red Hat Enterprise Linux had a polished GNOME 2 desktop.
- SUSE Enterprise Linux had a polished GNOME 2 desktop.
They were also using pretty much the same components. Since then, we had the MATE/GNOME 3/Unity/Cinnamon split and the upcoming X.org/Wayland/Mir split.
I'm skeptical Mir is going to be a serious split, and even then it'll be Mir/Wayland - both of those will still run X.Org apps via shim-servers, same way Mac OS does.
- Ubuntu had a polished GNOME 2 desktop.
- Red Hat Enterprise Linux had a polished GNOME 2 desktop.
- SUSE Enterprise Linux had a polished GNOME 2 desktop.
They were also using pretty much the same components. Since then, we had the MATE/GNOME 3/Unity/Cinnamon split and the upcoming X.org/Wayland/Mir split.