I don't see a 10 as "perfect in everyway", but more as in "I couldn't find anything to change". Doesn't necessarily mean it's "perfect", but I wouldn't know how to make it better myself.
I think that there are hundreds, maybe even thousands, of albums that “deserve” a 10 - just think of how many pure classics there are in the world. But I think your own score has to be somewhat personal, so I hand out relatively