I did not say it was perfect on either. I said they looked the same.
In DVD/BD Players (High End say OPPO) and High End Video Processors all kinds of strategies are employed to detect bad edit, mixed frames etc., all the kind of stupidity that can be done. Many of these strategies are largely successful but they are not magic. Even if they can detect a stupid combination of this and that it takes time. You will literally see bad deinterlacing for maybe a second or two and then the video processing concludes, oh yeah I know what to do with that and it goes to work. Unfortunately if the particular piece of video goes from properly encoded and flagged stuff to that particular sequence that it takes the video processing several seconds to diagnose. You have good, bad, good etc deinterlacing. And if the video processor designers were too clever by half, you can get the wrong approach applied for all the right reasons. So basically these chips try to make real time analysis and as I said they hit the nail on the head much of the time. But when you have something really screwed up in the stream it is going to come out hosed no matter how good the processing.
I have a DVD of Steely Dan that is flagged incorrectly. I can't remember exactly what they did but some devices or PC hardware/ software if you set it to film it will deinterlace it properly. It used to drive me crazy trying to figure out how to get it played without artifacts. Truth was, it was messed up and when it was decoded and rendered correctly to the eye it was configured wrong on that device or that software. I never really tried to see what they did. I just know one Disc Player out of 10 it worked with no intervention and even something like a DVDO or Lumagen could not do it no matter what the settings. I don't how these devices decide whether to honor the flags or analyse the frames. In any case there is a lot of screwed up video and when the cable guys decide to squeeze a stream down further and they are using some sloppy generic interlacing, you can really get a mess.
Mits WD-92840 92" DLP - Lumagen Radiance XS, Martin Logan Motion 40s, Ascend Sierra 2s
Older 58" Panny Plasma -DVDO DUO, JBL Studio 530
Pioneer AJs, PSB Images, Usher S520, JBL HLS-610, Definitive SM45, MusicHall Marimba