I feel like we need to properly define some terms here.
Upscaling is when you take a fixed render resolution (like, say 640x480) and forcibly expand it to fit a larger resolution (like, say 1920x1080). Conversely, this process is also called subsampling. This process only improves the end picture insofar as it fills your display; the picture is still essentially the exact same as the original render size (in this case, the 640x480). The only thing that would happen if no upscaling occurred would be the picture would be surrounded by a black box with the original picture sitting in the middle.
Native rendering is the case in which the picture is made at the same resolution as the end display; in which case no scaling is necessary. With this method of rendering, many more details can be observed in the picture thanks to the increased render size.
For an example to illustrate the point, I'm going to use some screenshots from the PC version of Dark Souls.
This is an example of a subsampled 1080 render: [1]
This is the same shot rendered at native 1080: [2]
It should be fairly obvious that the natively rendered picture has the advantage of sharpness and increased, well, picture resolution.
There's a third case called supersampling, but that's largely irrelevant to game console discussion.