Where does this assumption come from that Kos is so much better at grappling than GSP is? I've yet to see any evidence of that. Spout all the amateur wrestling credentials you want to, but I don't see how Koschek will be any more successful at handling a properly prepared St. Pierre than Matt Hughes did.
Hughes was still acknowledged at the time of his second fight with Georges to be an excellent wrestler and one of the very strongest fighters in the welterweight division. Yet his takedown attempts against GSP proved futile. St. Pierre's losses have been the result of gaffs on his part, first hanging his arm out for Hughes in a fight he was doing well in, then leaving himself open for the punch by Serra.
And unless he gaffs again, he's not gonna lay there with Kos on top of him and not do anything.
Does Koschek have a chance? Of course. If Serra-St. Pierre taught us anything, it's that anyone can win on any given night.
I truly believe this is Rush's fight to lose. If GSP comes in as the confident, composed fighter who manhandled Hughes, bullied Sherk and made Trigg look like a little girl, then ol' Kos is in trouble.