lpg i prefer road bikes, but disc brakes are superior (so safer), and most people have only ridden MTBs so they like the stability/ease of flat handlebars (hence the popularity of flat-bar road bikes)
also(!) track bikes sometimes haven't got brake holes. disc brakes = perfect solution! I think a superskinny 700C wheel would look cool with a disc rotor on there...
Where would you mount the caliper ?