Folders might not have a longer wheelbase, but for the same wheelbase as a bigger bike, there will be less wheel sticking out either end by a couple inches. Smaller wheels also mean less weight further out, which has all kinds of benefits in the tight confines of urban traffic. If you like "threading the needle" through traffic, a folder or mini- does better in an urban setting -- once traffic speed picks up, opens up, and the frequent stops get less frequent, a road bike might be the better tool for the job.