Photo by NCinDC This is a question I often ask myself when strolling by the intersection of 14th and U Streets NW (though thankfully a little less often now, since the long-awaited redevelopment of the buildings on the northeast corner nears completion). Matt Yglesias offers up the vacant building next door, however, as a case study in why, even accounting for the current recession, so many city storefronts in seemingly ideal locations remain vacant…