Now that you mention it, I was somewhat curious. I ran the following simple query on both Super User and Stack Overflow to see how many users had edit permission (>= 2000 reputation):
SELECT
COUNT(*)
FROM
Users
WHERE
Users.Reputation >= 2000
Which returns 488 for Super User, and 18890 for Stack Overflow. As a percentage of total users (i.e. commenting out the WHERE clause in the above query), and repeating the query for Android SE while we're at it, we get:
Super User: ( 488 / 136571) x 100% = 0.357%
Stack Overflow: (18890 / 1582958) x 100% = 1.193%
Android SE: ( 32 / 19260) x 100% = 0.166%
Given these numbers, it appears as though Super User has roughly 3.3 times less editors as a percentage of all users on the site as compared to Stack Overflow.