Where we lived before we moved here those were required. They actually fined you if you didn't comply. Some folks still had decorative wood numbers too.
I think if I were doing wood/pvc numbers choice of material might depend on the size of the numbers. If they were real big where checking/splitting would be much less of an issue, I might use cypress or cedar. Nice clear cypress is available here so that is what I'd use for big fat numbers. I guess the size would depend on how far away they were expected to be seen and read from. Cypress holds up to the weather really well as does cedar.