First, while many natives thrive in sunny and dry conditions (think: chapparal habitat), others grow along seeps or in other moist conditions. A fairly large number of the most attractive natives are from the Channel Islands and are used to more fog and more moisture than even the Bay Area, never mind Southern California.
More importantly, all natives are watered fairly regularly in the nursery, and they need the water when they are small. Mother nature, only keeps around the top 10% of seedlings, if that, but nurseries (and even us mice) like to keep a larger percentage so we cheat by watering. When you transplant your beauty from the pot into the ground, it therefore needs water initially to grow roots and to thrive. It makes me want to cry when I hear people stick their little treasures into the ground and ignore them for a few months, then notice they've died and are indignant. That's really frustrating for the people, and even more so for the plants. Interestingly, Tilden Regional Park Botanical Garden does not even put a label on a plant until it's one year old. Of course, they have many rare natives from unusual climate conditions, including plants that grow in the Sierras. Those plants are really hard to acclimatise to the East Bay conditions. But I do find that in my own garden, the first year is the danger zone. I water about once every 10-14 days, and might do a little spot watering if I find things are really bone dry using my moisture meter.
Finally, after 2-3 years, most of the natives that do well in hot, dry conditions can be on their own. Theoretically. Except that experience has shown that cutting off water won't kill the plants, they do look a lot better if they get some water every 3-4 weeks.
So, while native absolutely get by with a lot less water than many other plants
- Some require water year round or go dormant (some ferns will do that)
- All need regular water in the first two years
- Most look better with at least monthly water in a garden setting