It's because the scale is small. The size is set to 80x80 pixels, presumably for icon exporting. However there's nothing stopping someone from opening it inkscape and exporting a PNG at 12000 DPI (which results in a 10k x 10k raster resolution). I don't think the logo scale should be so small and I don't think browser should have such limited zoom capability. I place the most blame on the browsers though.
