Yes, you need the ability to draw content at fractional pixel offsets to get smooth motion. That's different than the "subpixel rendering" the original post was talking about, though, which is a way to draw sharper shapes (usually text) by addressing the red, green and blue "subpixels" individually: https://en.wikipedia.org/wiki/Subpixel_rendering
Except that they are functionally identical. In order to draw at subpixel offsets you need subpixel rendering (or rather: if you have drawing text at subpixel offsets without proper subpixel rendering you get really bad artifacts)
Your claim that you get really bad artifacts on a retina display when you draw lines properly is also needs citation. I don't know if the retina display has enough pixels to meet the claims either, but it seems you're confusing anti-aliasing with subpixel rendering.
It is possible to show, however, that if a scene has a band-limited detail property and the join response of your visual system, your eyes' point spread function and the pixel geometry resembles a Nyquist pulse, then indeed there is a density (which would be equal to the density where 1 pixel is covered by 1 sampling element in the retina) which is sufficient for perfect reconstruction of the image, even if it is moving.
All you need is regular antialiasing, not subpixel antialiasing. To be precise about what I mean: drawing a black line on a white background with regular antialiasing will produce only black, white and gray pixels. Subpixel antialiasing will produce colored pixels. What I'm saying is that you don't need the colored pixels to produce smooth motion.
