I think my display is actually 720p. But the point is the flickering effect is the same in all resolutions, it's just more noticeable in the higher resolutions.
I guess what I'm saying is that on the smaller SDTV the picture looks more "real" simply because the resolution is not high enough to draw so much attention to the shortcomings of GT4s graphics. One example of this is the trees on the courses. On a SDTV they look a bit indistinct & blurry but the eye reads them as "realistic", in a higher resolution you can clearly see that they are flat & rendered.
One thing I've noticed in general, is that in video games, less is often more: the eye (or brain) will fill in visual information that is not there, but if there is visual information that is not true to life, the eye (or brain) immediately notices it. That's why HD is a challenge: by providing so much information, it really raises the bar on what needs to be rendered in order to have the illusion of reality be convincing.