Well I wont bother with putting them on the list for the new boat, as that will either be rod or PBO. If they wont do rod, they certainly wont like PBO rigging.
I suspect that it is to do with the lack of warning that rod gives of failure - but then stainless wire doesnt give any useful warning either. Perhaps it's just that most rod is fitted to higher performance rigs, and as such may be pushed harder. Ther again, that is'nt true as my current boat is a big fat cruiser that doesnt get thrashed - it's just the weight saving over stainless wire was significant.
PBO or Zylon (technically it is poly—phenylene—2, 6—benzobisoxazole, ehich may be more detail than any of us need to know!) is one of the modern wonder synthetics. Very light weight, very low stretch. For a high performance boat the benefits are significant as the weight of rigging is only 20% that of rod (which itself is less than wire).
Depending on the terminators / chainplates you can also avoid metal/metal connections, which are always bad for corrosion and chafe issues.
Sounds as good a justification as anything for biasing me towards wire standing rigging on a mast I will shortly be rigging.
The other factor is cost, my friend had to replace one lower on his 35 ft French yacht. The total cost of the one piece of rod was about £500. I shudder to think what PBO would cost.
Unfortunately state of the art performance always comes at a price.
Perhaps, one day an equivelant to PBO will be the norm but until then I think I'll stick to stainless wire.