@Enough I agree, Ive been doing large enterprise IT work (very large) for a over 10 years and IT in general for 30. Its like Blizz tests he functionality of the updates but not the delivery. Since I have to guess that they have tested the code update internally as well as on the PTR the only reason for these update delays is the lack of testing of the delivery process. Where I work, an omission like that would lead to the update not getting approved and everything would have to go back for additional testing for the update process itself, its length of time, change file records (before and after) along with any other required metric to determine if the update was successful, in the amount of time expected. Its not rocket science, its due diligence. Its a linear process that should be automated and only requiring a human to initiate the task script(s) when directed.

1) Bring system off-line (end connections and prevent new ones)
2) Backup data
3) Test back up
4) Apply update(s)
5) Test/Confirm update results
6) Bring system on-line
7) Enjoy.....

Whether for 1 host or a 1000 the process doesn't change, only the scope. At a guess it looks like Blizz does too much work manually allowing the gnomes and goblins too many opportunities to use their grubby fingers. Then again, maybe they employ Taurens to do the updates, that could explain the stunned servers in the data centers.