Making world doesn't change all ownerships?

[Francisco Reyes]

I have a test machine where some users changed a number of 
directories to be owned by "www:www" by mistake. The machine was unusable. 

After rebuilding from sources the machine was usable, but I noticed that 
a number of files still were owned by "www". In particular I saw files in 
/usr/sbin, /usr/bin.. and likely other places.

Shouldn't rebuilding from source fix the ownership?
I followed the steps in  "Common items" from /usr/src/UPDATING, like have 
done many times before...

        make buildworld
        make kernel KERNCONF=YOUR_KERNEL_HERE
                                                        [1]
        <reboot in single user>                         [3]
        mergemaster -p                                  [5]
        make installworld
        make delete-old
        mergemaster                                     [4]
        <reboot>

Since it is a test machine, if there are still odd issues I may just re-do 
the whole machine.. and newfs.. but was puzzled that rebulding world would 
leave binarines with the wrong ownership.