Actually I interviewed as a native english speaker with GRE scores higher than the median on the site so I doubt it was for only english-testing purposes. Not only that, my interview email from the GSD stated that invitation was based on exceptional credentials, the interview is to narrow down the applicant list, and furthermore during my interview it was explicitly stated that I made the “short-list” of applicants thus they are using the interviews to learn more about those select individuals and it is indeed a deciding factor.
