First, let me explain that I am now back in the CS after about a 2 year hiatus. After reading the journal article and all the replies here, I guess I want to put in my 2 cent piece and reply.
My feeling is, what has happened with the Presidential dollars is no different than what the Sac dollars have gone through. Thanks to 6 Mile Rick, my Sac Dollar proof set is complete thru 2015. I have been working on the set off and on since 2006. When I first started, I bought a 2001-S Proof graded PF-70 Ultra Cameo. At the time, this coin, in this grade, had a Numismedia value of well over $200, and that is what I paid. Well thru the years, the price guides have decreased their price on this course by over 50%. Why? Because as a few people have mentioned, there are a lot of coins being held and just now graded, and more PF70Ultra Cameo's have been graded.
So, what does this do? It's supply and demand. When the supply exceeds the demand, a coin's valuation and point total goes way down. All modern coins have this happen, although possibly not to the same degree. So to get on NCG's case and say they're duping us, to me, is not right and very unfair to NGC.
I tried to make this same point to a certain person on this board. Many of the older veteran's here probably remember him. Paul is his first name and that's all I'm giving out. He was getting on another member for not buying PF 70 Sacs. Called this person dumb etc. and I called him on it and he could not understand that the coins were being reduced in value because more were coming on the market.
I am not trying to bash anyone, just trying to make all of us understand on modern coins, I feel this problem is not a problem, no one is trying to dupe us because this is a fact of economic life.
Thanks for reading and I hope I have made my point in a clear manner.