It includes an additional charger, wich costs 25$ in the ifixit store, + has both hdmi and Displaylink, both of wich can reach 4k 120hz. Also 1Gb/s ethernet port and 3 usb 3.1. Also firmware updates and support from valve.
X11 because my current setup on Wayland crashes constantly, otherwise always Wayland.
And there’s the attempt at discouraging you from going bare-metal.
I doubt that “few developers choose this” is true.