Keirin is a very high intensity sport, with quick explosive races every hour. The athletes must be very clever and skilled, in addition to very fit and determined. It's hard to say however how much is planned in terms of who is intended to win, and who is intended to "almost" win...but that's another story.
One cool thing that I learned about Keirin is that competitors actually go to a proper training school with fitness training and classes alike. It is a major life dedication to be a bike race competitor, as the training and commitment is close to the military in terms of intensity. Not all students will make it through this basic training, so in a way it a filtration system to only allow the most determined and able students to make it to the professional racing world.
Here is a link to a training school walkthrough: