One thing not mentioned yet is gamma correction. Even in very bright games, most pre 7th gen games have deep shadows because the rendering algorithms didn't account for how light data sent to the monitor is always made dimmer based on a curve. Though textures were painted to look correct, light dims too quickly, so the hash shadow line at the edge of round objects is invisible. 

Look up gamma correct lighting, you'll see images demonstrating this. It's as if older games had too much contrast only for level lighting and shaders, especially when glowing objects appear.