Thing is GtoRA they rarely are that badly hurt though I guess it depends what you call badly. Its not uncommon for a guy to race in a cast or with pinned bones. Heck one guys once completed the Paris Dakar Rally with two Broken ankles. Generaly only a spinal injury or serious head injury is considered bad. Basicaly if it stops you riding for good its a bad injury otherwise it doesn't count. Those guys are real tough. Most wear race gear that will protect. With the exception of Lazs that is ( kidding ) Good leathers a back protector helmet etc can prevent most serious injury.
And on a final note that vid is one of the reasons why Moto GP beats that boring procession called F1 every time as a spectator sport.