Also, on those forks, isn't the axle able to move relative to the brakes on rim?
No, if you look the brakes and the axle are on the same piece of metal, meaning their relationship is fixed. The fork pivots on the two pairs of pivot points by the axle, moving (relatively) linearly up and down with the aid of the shock unit on top of the front 'pair' of forks. A fair bit of stiction from the numerous pivots, but their stiffness and large bump performance were leagues ahead of anything else at the time.
I didn't realise Thompson posts had been around that long - I suppose I'm surprised they took so long to get real recognition.