Ok, if you want to be really pedantic about, I guess 'inherently' is the wrong word to use. Yes, you can encode a progressive frame on a DVD (just like you could encode a progressive frame on a CD if you wanted), but it's meaningless. The fact is, it can't be played back on a DVD player as such because MPEG decoders decode in an interlaced fashion. The only way to get a progressive signal out of a DVD player is if it uses a separate chip to deinterlace AFTER the interlaced video has been decoded