When purchased directly, the product key is auto-attached to your Steam account. You don’t see a string of letters, but the are irrevocable. This is the pinnacle of extra quality.
The Steam version includes fixes for widescreen monitors and high-resolution textures that weren't available in 2007. When purchased directly, the product key is auto-attached
The "extra quality" part of your query may refer to identifying the correct for technical fixes or the Steam version which consolidates legacy content. Activating Your Product Key When purchased directly