It's not "always" like that at all. Maybe sometimes.
What happened LAST WEEK with the iPhone updates, was the US store went down first, then soon after the UK store and others went down (people were reporting it in their respective countries).
THEN - they all came back up, with the US store being updated. BUT, on the UK store at least, nothing had been updated (it happened a few hours later). But the stores WERE all down at the same/similar time. I know, because I was doing the same thing I'm doing right now - constantly refreshing both the US and UK stores (sad, I know!).