Miami is a great food town, of course. Most famously for the chefs who fuse Caribbean foods into a mango-habanero mojo of New World cuisine. Less exotic, but still welcome in the mix, are the cheese steaks and inimitable pizzas transplanted from Philadelphia and New York. To this Americana end, at long last, Miami can add the hot dog. Make that the authentic Chicago-style hot dog. Mr. G's USA, a humble joint new to town, keeps it real: A Vienna Beef wiener served on a steamed bun with onions, mustard, relish, peppers, tomatoes, celery salt, and absolutely positively no ketchup. A bit of Midwestern mojo, if you will. Each substantial dog costs $2.75, and usually comes with either free fries, free soda, or both. Open Monday through Friday from 6 a.m. to 8 p.m., Saturday from 6 a.m. to 9 p.m., and Sunday from 6 a.m. to 12 p.m. There are other food options at Mr. G's, from ribs to Greek salads to a breakfast eggs Benedict. But why?