In the last few years, the average computer screen size increased a lot. It means, that more and more people have 20"+ displays. Currently, your wallpapers are just a little too small to fit these screens without losing quality. Because of this reason, I suggest that you should increase the resolution of the resolution of the dowloadable wallpapers. Maybe, just upgrading to 1680x1050(20",22") or even 1900x1200(24") would be a lot nicer.