There are only two reasons for the store being offline:
Apple want to generate hype around any new products; or
Apple are shit at programming and can't write decent code to save themselves - there are plenty of ways of staging upgrades that don't require the type of outage Apple insists on, inless the code is very badly written.
Now I know how bad iTunes is, and I know a lot of the linuxbois will diss Apple at the drop of a hat, but really Apple Marketing, do you NEED to take the store offline and piss off your loyal customers? Or do you do it because you *know* the fanbois will come back and buy your products anyway?