I think the whole idea has always been to limit the number of New Yorkers (Bostonians, DCers, Miamians, etc.) who are willing to stay up and place that order in the first few minutes, so that servers aren't too overloaded. (Making things tough, but not quite as tough, for Chicago, Denver, and L.A. then comes as part of the bargain.) The Eastern Time Zone is just the one that makes the most sense to suppress, and 3 a.m. is right around the sweet spot for making things difficult for first-day customers.
Going forward, thoughand perhaps with the Watch more than any other productthe above might not be the case anymore. How long until the numbers from Hong Kong/Shanghai/Beijing/etc. (UTC +8:00, 4:01 p.m. for the to-date standard launch) swamp the U.S. East Coast? Will Cupertino start introducing products at 11:00 a.m. or noon Pacific on launch days, in order to stick China with the 3 or 4 a.m. opening?