Maybe at large companies, but at small companies in California, this has not been my experience. Plenty of employers realize that programmers tend to program on the side, and as long as you don't use company hardware or facilities, they claim no ownership of your IP.

This hasn't been my experience. My current employer doesn't have a clause like this, and although they wouldn't have needed to, they also in-writing cleared my side-projects when I joined, even commercial ones.