Because he is not so good when it comes to the slower claycourts and his opponent is a decent claycourter. It is like Davydenko is the fourth seeded now and when we have our short grass season coming he hardly is favourite against decent grassplayers when his record is 1-9 on grass. Roddick's lifetime record on all courts is 415-128 but on european clay he is "only" 32-26. Just my opinion but I hope it explained something.