Gentlemen, keep in mind that Keirin bikes are NOT the state of the art track bikes (for some reason BF is convinced that they are...along with Brooks saddles and MKS pedals). Those racers use those bikes because they HAVE TO. They are regulated (and hindered) by the sport's governing body. They do so because Keirin is a gambling sport in Japan like horse racing is in the US.

When those same racers compete in other races, international races they don't use the Keirin style bikes.