Thanks for the reply. After my original post, I found this site, which has a different take: http://www.know-your-keyboard-piano.com/yamaha-pianos.html
"The Yamaha pianos in the higher price range feature the Yamaha Graded Hammer effect whereas the models in the lower price range feature the Yamaha Graded Hammer Standard effect.
So what is the difference between the two?
Not much except that the Yamaha Graded Hammer is slightly better built and slightly faster than the standard version. Hence they are available in the higher end pianos!"
Yamaha keeps changing the names they use. Today there are three actions used in Yamaha's mass market DPs. They have replaced GHE with GH. So there are now three. But Yamaha has not updated all their material.
1) "GST" -- NP-30
2) "GHS" - P85 and others
3) "GH" - P155, YDP 233 and others
Go to this web page and then click the big blue square on the left that reads
"Video Comparison" there look at the set of four buttons that describe the three actions. But do notice the video is OLD it contains two discontinued models and does not show the new P155 and is still using the term "GHE" rather then "GH". But otherwise it is the best source of info.http://www.yamaha.com/yamahavgn/CDA/List/ModelSeriesList.html?CTID=205900&CNTYP=PRODUCT
This list will change soon when the CP1 and CP5 hit the stores and the "NW-Stage" becomes available as a fourth option.
Also there are some other actions available in the clavinova line.
If you want to read more the yamaha.com web site is likely the more authoritative source. You can download and read the user manuals. With effort you can find the support site where they sell parts, there are exploded diagrams there of the key actions. Few people care about that level of detail