It might be the new "high-strength steel" being used to save weight has slightly different forming characteristics (spring-back, etc.) and sometimes the old rules-of-thumb don't produce quite as good results as the older, thicker materials without a little bit more iteration (read development costs here) in the design cycle. They are shaving weight by using thinner steel, but now the panels are more vulnerable to denting from smaller forces. Like how my door sill dented instead of breaking my shin. But the truck IS lighter than it would be if they used the older. thicker materials. But the newer materials are less forgiving to work with.