It seems to me that Dual owners might be trading up because the 12 series looked more precise and modern than the 10 series, where as the Garrards that followed the Lab series just looked cheap. They might have been as good or better, but they sure didn't look it. And if the aesthetics of the Lab series appealed, the new ones would not.
Read the 1964 review from "Gramophone" regarding the Lab 80. It has its charms. The link will take you to the first page of a long article consisting of reviews. Go to the bottom and click on page 8 and it will take you to the beginning of the Lab 80 review. I'm charmed by it...
http://www.gramophone.net/Issue/Page/November 1964/107/805510/TECHNICAL+REPORTS#header-logo
, where as the Garrards that followed the Lab series just looked cheap. They might have been as good or better, but they sure didn't look it. And if the aesthetics of the Lab series appealed, the new ones would not.