Even the great Reagan used to quote him in admiration, so does Bush.
I am not certain if they really do think that highly of him or just know it is pointless to not praise him.
I believe you have nailed it. Some were placed so high upon pedestals, and praised for so long, before their warts were discovered, that now they are untouchable.
Considering how many of those untouchables were already set in stone before President Reagan came along and him being rated at # 8, I don't believe it would be unreasonable at all for us to presume that if all positions were open and the ratings were today, President Reagan would more than likely be placed within the top five.
Dang! that is one long sentence, but I couldn't find a stopping place.