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.

Yes, sometime even twice a years, but get them changed once you notice a very tiny play when checking the Brompton (catching it early greatly helped the poor mechanic who have to deal with your Brompton).

Left for too long will result in a new rear triangle (due to material have been eroded to almost paper thin), even a new frame where the hinge have worn it out to the point that a new one cannot be fitted.

The example I provided above were from customer bike that have not been service for around 5 years, and Brompton are designed to be a continual improvement product, making them keep their value up for longer.