It's not that simple. Normally you render significantly upscaled stuff in an off-screen buffer and then downscale it for the best possible appearance for every single frame. There are some ratios you need to keep, or you'd end up with Linux-style graphics "quality" (try scaling factor other than 1.0). If you just scale icon/bitmap once without thinking about this, it would look most likely ugly after upscaling/downscaling steps (unless you got lucky).
It's like when you learn how to notice aliasing artifacts in photos taken with DSLRs. It cannot be unseen. So even if those issues are mostly noticeable in low-res, you "cannot unsee" them in higher resolutions anymore either.
