I have my comcast cable box set to "native" output. I don't want the cheap cable box messing with the signal fed to my expensive TV. In fact, I replaced my cable box and got weird green shadows on some shows until I set the cable box output to native (it may have been 480i or 480p by default).
I haven't changed the "format" setting of my tv, but, with the hdmi input, it automatically resizes based on the input. I don't think it is just stretching either, or, perhaps it stretch algorithm is different than my previous TV . It seems to be zooming in as well. My only negative is that it takes a few seconds when I change channels that are not the same resolution.
Stan