i would think if you have two brakes foot retention, although nice to have, isn't SUPER necessary on a fixed gear.

although, personally speaking, when i bomb down hills on a fixed gear bike (i have a low gear setting so i spin like crazy) i would definitely want foot retention on a fixed gear bike, however many brakes, just because the way the peddles start spinning i would not want my feet to be bucked off the peddles like a bull bucking a bull rider and have my feet in the air with the peddles spinning frantically...

maybe they just have coaster brakes? i have a coaster brake 700c bike, skidz for days!