Retail depends on much more than the amount of residents within an area. Traffic and location is more important to a retailer. The demographic of their potential customers is also important. (One thing Detroit still has to conquer.)
Another thing, don't underestimate the power of the Super Bowl. Half of Downtown Houston was empty, with the exception of a drive-thru McDonald's and a drive-thru Bank-One, about a month before the 2004 Super Bowl. By the week before the game there was little to no vacancies.
There's going to be a lot of companies that will be more willing to test the water in Detroit, simply because of the Super Bowl. It gives them the impression that if the city can draw in these type of events, that business will be booming.
~my 2 cents.