The only posts I have ever read that say they also add 1/2" are when they measure them and see that they are the same length as the 5100's or they are 1/2" longer than the OEM ranchos. But occording to norcal (who got it from greg) something about the spring perch causes them to keep the stock ride height. somebody correct me if I'm wrong but thats how I understand it from what I have read.
PRG told me the HD's don't provide additional lift, and the reason the 5100's do it from the bottom spring perch position being higher than the HD's, not due to length.
I think the HD's are very close to the stock '04 4x4 off road pkg Ranchos, because with a 2.5" leveling kit I still have a little rake, but when I had my truck at 3" total, with DRE/Icon coilovers and a custom 1" spacer, it was level. So if the HD's did add a 1/2" my Titan would have been at the same 3" with a 2.5" leveling kit.
I really couldnt tell you whether or not its the struts that are causing the 1" drop, but I do know that your stock struts are completely shot after 90k miles. A lot of guys on here have been having to replace them after 20-30k miles. I still have my stock front struts on and even though they still ride good I'm sure they are not what they should be. I replaced my rear shocks at 20k miles when I put my lift on and they were completely done. If you like the stock ride height I would say just throw some HD's on there and see what that does for you.