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That's not entirely true. Lion full screen can work that way, but it doesn't come entirely for free. I believe that Sublime Text would need to create an additional window per extra display, set the NSWindowCollectionBehaviorFullScreenAuxiliary style on them, and set their size/position to cover the display they are for. I'm not saying it's trivial, but it's doable without writing full screen from scratch. :)

An example of an app that does this is VMware Fusion.