however the real world sucks, most field bugs are caused from configurations you would never think of and a ever changing world

i.e. apple just recently decided to break 5 years of responsive design practices by ignoring the maximum-scale meta tag. their decision is not without merit, but suddenly many web applications started behaving weirdly and encountering usage pattern they were never tested on before.

those edge cases never existed before, but I bet only the shops with dedicated testers caught them within the first week.