Minimum Forming Thickness

We noticed that minimum thickness after forming is 6 mm as per Part 7 of ASME VIII-2 Edition 2004 and it is changed to 1.6 mm in New rewrite edition 2007. How does this affect fabrication of pressure vessel....?

Usually all the vessel having minimum dimensions (thickness of shell, head, nozzle) are far greater that 6 mm, then then the change like this really affect?

I am looking forward for your valuable guidance.