There are all kinds of crazy resolutions and aspect ratios available on monitors nowadays, why lock VSR support down to only the most popular kinds? I can't use VSR with my monitor, simply because it's not one of the 4 or 5 most common resolution/aspect ratio combinations (i.e. 1080p 16:9).
With Nvidia DSR, it gives you super resolutions that are are factors of your native resolution, like 1.2x, 3x, etc., no matter what resolution it is. It's that simple. They've had this for six years .