I watched the first half of the The Good, Bad, Weird last night, and I immediately could tell that it was recorded in 1080i. (Easiest for me to tell with larger scale outdoor pans, and that's how the movie opens IIRC.) So I see that this is simply how the US bluray is recorded, wtheck. I think foreign versions get the progressive?
That said, for being interlaced, it's as good as it comes. I bet that if it was given as 1080p, it would look really really top notch.