Editor's note: Happy to report that the post title is no longer true. On December 22, 2010, the National Academy of Recording Arts and Sciences (NARAS - the Grammy people) announced that the Kingston Trio was to be given the Lifetime Achievement award on 2/13/11 - and this is essentially the Grammy HOF.
The following chart facts were culled from Joel Whitburn's Top Pop Albums, the 2001 edition. Whitburn and his Record Research, Inc. are about the last word in accuracy about record sales charts, and he has a new edition of the book just out.
The dominance in the last decade of Jay-z and other hip hop artists suggests that the KT's rank may slip a bit in some of the categories below - but some are cemented in history, like "most weeks with a charting album by decade," where the KT's rank is permanent.
Note that most of these chart summaries refer to position on the charts or appearance on them and do not refer to total record sales. Still - very impressive.