[locate individual high contrast pixel] != [ability to distinguish individual pixels]
Vision and visual acuity is not this simple. See, e.g., http://www.michaelbach.de/ot/lum_hyperacuity/
I don't actually know, but perhaps seeing something as pixelated requires being able to resolve the edges of an individual pixel.
A better test would be to see if people can detect a difference in the pixel "phase" (for lack of a better word) of some pixel-drawn object (that is, show identically shaped objects that have a different internal pixel organizations because of their position on the screen). Do an ABX-style test, see if you can tell the difference.
I'll bet you can tell the difference on a classic display. I'll bet you can't on the iPhone 4+.
[edit: made the comment slightly nicer ... :/]