The point is you sell a product, it better be what it claims to be. I didn't buy SPF30, I bought SPF50. When I made that choice, I expect at least SPF50. But

The point is you sell a product, it better be what it claims to be. I didn't buy SPF30, I bought SPF50. When I made that choice, I expect at least SPF50. But you are also dismissing a 25% difference in total transmitted UV - and that's before degradation in the field due to usage and practical concerns, which is why we want SPF50 in the first place.