I don't think that this is true. Just because other people have played less games in the field than Ortiz, does not mean that there are a ton of DHs that can play good defense (I can't remember a non-interleague game where Ortiz was the first baseman).
Of people with minimum 50 PAs as a DH, Michael Young wasn't signed to be a DH (and isn't a good fielder regardless), V-Mart was signed to DH and be an occasional catcher, Hafner is definitely a no-glove DH, Butler was moved to DH after Hosmer was called up, Kubel is terrible defensively, Giambi does play some first (but isn't really a DH since he plays for the Rockies, all the DH at-bats probably came from interleague play), Damon plays for the Rays and they do weird stuff, Abreu is no longer a good fielder, Thome only DHs, and Posada/Guerrero/Matsui can't really play anything besides DH at this point.
Basically, everyone on the list was either pushed out of their position by a better player, or is terrible defensively (or plays for the Rays). I don't see any concerted move towards DHs that are considered good defensively, and I'm not surprised, since teams would have to pay extra to sign those players (while they can lowball players like Guerrero and Ortiz since they provide no defensive value).