It's just for its awards chances, as LA and NY are where most awards organizations and critics groups are based. Most awards season films employ this release strategy.
A lot of people are predicting an Oscar nom for Robbie now.
Also: a LOT of the voters in the industry who choose the nominees are based in LA / NY, so it would reach them. Studios do screenings for films just for Academy members (via my friends in Hollywood who tell me this), and if they don't or can't get to them, they can go to a cinema not too far away. Studios do send screener DVDs to voters / members of the Academy who are not in those two cities, e.g. British members who live in London, productions in Canada (Toronto / Vancouver are the two major cinema hubs up here), and other foreign Academy members like Marion Cotillard, Audrey Tautou, Juliette Binoche and Kristin Scott Thomas, all of whom are based in Paris along with the winning team from 2011 Best Picture winner The Artist. But the concentration seems to be on cities where the film industries are based, so that it captures the largest concentration of professionals and critics, at least geographically.
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I think the fact that she's already been to every premiere tells us that she will definitely be there.....
I did see her just yesterday all over the news posing with the cast at the premiere!