Codswallop. The Challenge is a legimate way of finding the top 15 riders in the world and should be open to every rider. Those who finish 1-2-3 deserve there spot in next years series.
Riders do not know if they are performing poorly in the GP series before competiting in challenge qualifiers so your theory is flawed. Vaculik doing very well, Iversen not far off top 8 so Zagar the only one in danger but he is only 13pts off top 8.