Losing IS considered normal for Federer at Masters events and lower. At Grand Slams, it is still not normal, because it still doesnt happen (except against very top players at semis or finals).
that's true but it should also be taken into account that federer was slightly lucky in RG and Wimbledon. In RG he was on the brink of defeat against Del Potro and Haas, and in Wimbledon he almost lost to Roddick, a player that he would have had no problems defeating on grass a couple of years ago. I would say that perhaps Federer wouldn't have won had he faced any of the top 4 in either RG or Wimby... especially in RG.
in any case, I don't deny that Federer gives the best of him in the GSs rather than in the MSs. It would be highly unlikely that Federer would lose to a guy like Wawinkra or Tsonga in a GS event.