In theory this matters, because we could load the perfect image size for our element, if only HTML could. But in practice: 1. You wouldn't want to have thousa

In theory this matters, because we could load the perfect image size for our element, if only HTML could. But in practice: 1. You wouldn't want to have thousands of slightly different size variations of the same image generated and cached on your CDN/server. 2. You would quantize and keep a few sizes (like small, medium, large, xlarge). 3. Once you do this, screen size becomes good enough of a heuristic to figure out which of the above set of quantized images you need for an element. 4. Ergo, all is as it should be.