That's actually evidence that Storybrook is in our world. To get from FTL to our world takes fairly spectacular magic...as far as we know, it's only been accomplished three times...ones with the beans and twice with the cabinet, whose magic was used up by those trips. Plus once for the curse, which apparently destroyed FTL. Getting from Storybrook to our world is trivial, although the curse seems to make it more difficult for FTL folk to manage. But as LooseWiring points out, the trip is made routinely. The curse made Storybrook a different kind of place in ways that are not entirely clear. But it IS clear that it is a different kind of place in our world.