As far as I know, no. I learned about this when I lived in North Carolina. The house I grew up in had 2x6 wet walls with all other walls being 2x4.

It could be state or local building codes based. Here is a mention of it from a city in Illinois. But it definitely isn't just a California thing.

https://elmhurst.org/DocumentCenter/View/1826/Plumbing-Requi...

https://www.reference.com/world-view/standard-wall-thickness...