Lets not be stupid here.
Dave only rated matches on a 4 star scale up until the early-mid 90s. He's said it multiple times that he revisits his rating system from time to time to see if he needs to add a star or not.
TV shows, movies, books, comics, games and much more are often rated on 1-10 scales depending on who does the rating.
To say that 5 stars is the end all be all is not only restrictive, but sends the message of "My opinion matters more than anyone else".
If Dave wants to rate it six stars let him. It isn't like he is going to spam 6 star ratings all over shows. It will be treated as a new, harder level of greatness to achieve even above the 5 star rating on his scale.