The water spots on a coating don't wash off. Even if you wash it once a week.
That is not entirely true. Go back to what exactly water spots are. Mineral deposits in the water that, if left will start a process of etching into clear/coat, coatings, and even wax. If through this scientific process of minerals etching into clear-coat, how would a wax stop this and a nano-glass ceramic coating wouldn't?
Here in AZ our water is mineral rich, especially copper. Yesterday we got a very dangerous (and deadly) dust storm. Typically during the monsoon season these dust storms preceded a down pour leaving your car looking like this:
Then factor in the AZ sun. Temps at 105 - 119 and an amazingly strong sun.
When we first moved here, I had a coating on my DD. We had our first monsoon, and when I washed the vehicle a week later I was dismayed to see spots. I even started a thread on this forum about it. I thought I did something wrong, or that coatings were useless. Determined, I didn't give up. I re-did the vehicle, but instead of one coat of the coating, I used a new bottle and did multiple coats. After the next three or four weekly washes I followed up with Re-Load. Since then, we've had amazing rains and dust storms, and I'm happy to report in over one year we haven't had one spotting issue.
Did this solve my issue? Was multi-coatings and follow up maintenance with ReLoad the answer? Will this work for everyone? I don't know...
One client came to us with his Audi R8 V10 peppered with water spots that were very persistent after a wash. After a light polish, using SpotLess on the plastics, and using this method of layering coatings, he was just back for his 6 month maintenance. He drives it daily so I know it's rained with dust storms since his full detail and during the maintenance It had a few water spots in the back, and they came right out with the wash.
Based upon my own personal experience, I would be reluctant to stand by your statement above.