OK, I might get attacked for saying this, and I might be wrong. But I have had a couple of recognized experts tell me thus:
NTSC is interlaced. It is part of the NTSC spec. Therefore, an NTSC DVD can only be interlaced. This would explain why, when I try to make a progressive DVD in Compressor, the resulting .m2v file still comes out interlaced. Try this by opening one of your own “progressive” DVD files in Mpeg Streamclip and checking the properties. In my case, it still says it is 1080i. DVD players are able to de-interlace a DVD and put out a progressive signal, but all NTSC DVDs are progressive to begin with.