When you rate a piece of art, you are able to rate everything at once Because you see all of it.  

Ratings for downloads are done when?  When youre sitting at the download screen.  all you’d have to go on is a promo picture.  How do you know this is a 5 or 3 Star freebie if  you havent even installed it on your system and started using it?   Even people can rate freebies without ever downloading it.