Yesterday, when I found Hatsune Miku: Project Diva F for Vita in Sony's E3 booth, I interpreted that as evidence of a North American release. After all, it was a game being shown at E3. However, that isn't actually the case.
Today, I went back to the booth and spotted a Sega rep next to the demo. He informed me that the game wasn't actually planned for North America; it was just being shown off at E3 as a demo. A brief image on a big screen inside the booth called it a "sneak peek" of a game coming to Japan.
In short, it was at E3, but isn't actually intended for North American release. That's quite unusual.