http://www.ricoh-imaging.co.jp/english/news/2012/20120911_8.html
So, it reflects less (claimed a 50% improvement) and the coated surface is harder. And it also says that the HD coating is "almost as good" as the last nano-tech Pentax original Aero Bright Coating which is of the highest grade previously. In the other words, Ricoh's HD coating is still not as good as the best Pentax'!
In fact, in the above press was released back to last year's Photokina. And it was already mentioned that "smc Pentax" would be replaced for all future lenses eventually, quoted:
"All future interchangeable lenses for digital cameras that equip this new coating will bear the name “HD PENTAX”, instead of the conventional “smc PENTAX”."
Now, they finally have taken the action only after one year for the "new" DA Limited lenses replacement, for what they said to do!
Still, as HD just stands for High Definition, this naming is just too mediocre and the marketing guy(s) who decided to use this name was/were really stupid enough! Yes, mediocre staff created mediocre names, that's it! :-o