Which strikes us as a little sad. Admittedly, the Gates of Ahn'Qiraj is a huge undertaking, and it would likely take a long time for the players on the new realm to get the War Effort over and done with (and surely Blizzard wouldn't want that competing for attention with any World Events planned for the next expansion). And even after the gates open, players can still complete that giant quest to get the Scepter anyway (just as they can right now on any other live realm). And as Blizzard says, most of these incoming players are coming from realms where the gates are open already anyway.
But it's still a little sad that Blizzard is stepping in to open the gates automatically rather than leaving the task up to the players. Just like all of the old world instances, Blizzard seems more than happy to leave all their old content and hard work behind, and instead focus players on what's coming out in the future.