Because the Europeans are such a whiny bitchy bunch Blizzard didn't want to have to deal with the walls of QQ from them. Even though it's totally possibly to have a worldwide release for WoW if they wanted.
In before eurotrash calling me an obnoxious american for pointing out simple truth.
---------- Post added 2010-12-05 at 05:39 PM ----------
Not true, the ruby sanctum patch hi EU servers first by virtue of being locked on US realms until the EU servers were up and running, then after downtime the US servers could get in to RS.