They're unlit, not dimmed on the XL as well, as in the video, they are still selectable and function as expected, I don't see any problems here, there's no difference between xl and non-xl here....
This really looks like it's designed that way and makes sense to me...:-
The buttons that are lit but dimmed do something on that screen e.g. show info, start stopwatch etc. and light up when you press them.
The buttons that are unlit (and not dimmed) change screen and are therefore don't light up due to that