The issue in a browser is that you have a default zoom that is often not 100% and you can also "zoom" in/out of web pages which by will cause blurriness or overly sharp images. If you decide to ignore that in favor of the native resolution, then the content size is likely too big or small for what the user expects and it's not clear what the user wants it to look like or scale to even if you did implement that too because of the huge variety in screen sizes and ratios the content could be viewed from.

A native application does not generally have these issues because by nature of being native it was built for the form factor it is being used on.