Brompton owners

And this pivot replacement is an annual event, is it?

Not for me, although on the old Rat Brompton I could feel the back end wagging from side to side under power due to the pivot bushes being well beyond their best-before date. How long they'll last depends how often you ride it and with how much vigour. I can't see any point in replacing the bushes (and the pivot bar if necessary) before there's detectable movement.