They're pretty damn close, modulo the Bayer pattern for most sensors and RGB stripe arrangement for most displays. Calling an LCD's subpixels rectangles is certainly an approximation that's valid on the scale of the distance from one pixel to the next.

> [...] and treating them as such (whether for font rendering, photo capture, rendering line drawings, or any other purpose) is pretty much always worse than treating pixels as a discrete approximation of a continuous image.

Whether treating those pixels as rectangles or points is worse depends as much on the software/analytic approach you're using as on the physical reality of their rectangular geometry.

> Unfortunately 2D approximation is inherently more complex than 1D approximation, so you inevitably get some artifacts even when you do fancy computationally expensive math, and the choice is about which type of artifacts to privilege.

True, if you're unjustifiably constraining yourself to treating computer graphics only with the methods of a generic signal processing problem. Bresenham's algorithm is radically simpler than anything involving Bessel functions and also happens to work very well in the real world both in terms of speed and visual quality. Adding antialiasing to it leaves you with something that's still extremely simple and is easy to explain in terms of pixels. An exhortation to never treat pixels as little squares is just plain wrong.