Actually, this is true much of the time. When a coin is sent back for a review of the grade, it is often returned AS IS with a statement that it meets their standards. However, there are also times that a settlement is made. One year at the Long Beach show I saw several dealers looking/bidding on a trunk of PCGS "buy-backs." I also know of two dealers who received "credit" on a # of future submissions at one of the "second tier" major services. It appears to be on a case to case basis with all the variables that suggests To the best of my knowledge, authentication errors are always corrected.
The market is the ones who hold them accountable. If they consistently do a poor job across the board or are all over the place all the time they quickly fade with their standing in the market place. ANACS is a perfect example of that and so is ICG. If they goon a coin its in their best interest to make it disappear or downgrade it which believe it or not does happen.
...and I DO truly appreciate authentication in slabs. Back when they introduced the things, I was happy. I thought they would mainly be used to prove a coin is authentic. Heck, I tell anyone who will listen to never buy certain coins like Trade dollars or certain key dates in anything other than a slab unless you are VERY familiar with the series. I LOVE the authentication aspect of slabs, but 99% of collectors concentrate on the grade. If they made slabs that authenticated coins, and maybe documented if a coin was cleaned or not, I would be a huge fan. Alternatively, if they actually graded to a Third Party standard, and WERE accountable to a standard grading system, I would have no issues at all. See, I agree with YOU on many things as well.
You might like to know this bit of numismatic trivia as it "mirrors" your idea...I learned in a grading seminar long ago that Charles Hoskins (former director of the ANACS Authentication Service and the director of the first coin grading service at the International Numismatic Society) believed that grading was a subjective, educated opinion. For that reason, the INS grading opinion was issued on a separate card from the INS Photo Certificate of authenticity. The second grading service at ANACS included the grade on the photo certificate. Years later, when INS began to use a large rectangular plastic "Photo Slab" the grade was placed on the label.
No way the coin in the OP would straight grade. The toning looks fake and with bright light the lines under it would be easily visible to the graders.
I've personally seen some very well doctored formerly cleaned coins that have been worked over retoned and straight graded. One case a 5 figure coin went straight at pcgs and then cac and was found to have been a cleaned coin that someone worked over and fooled the experts on. Another was the thread a few weeks ago about the cleaning details dollar that was doctored and went straight at pcgs these are only a few examples