Speculation for years has been that he might have a relatively brief time at the top because the style of game he plays is so physical and takes so much out of him. Until last season, he's always tailed off pretty significantly after Wimbledon. He'll still be a hell of a player for a while, but we may have a real tight 4-man (or possibly even -man) race for #1 in about 6 months to a year from now.