it was Rolex's daughter Tudor which uses ETA. Also, I have yet to see an AP with an ETA movement. And, I would like to remind that the original 1185 was a joint Piguet/Blancpain development. IWC uses ETA because they need exactly this: a very sturdy, reliable and proven movement design for their sports watches. An in-house movement is not necessary better technically than a mass-produced ETA which has been refined over the course of the years and the experience gained by volume.
Best,
Magnus