You know that Fed struggled against Nadal on clay because Nadal was still winning slams regularly when he was beating Fed. However, when Fed loses against someone who at the time of the loss is a non-factor (nevermind a consistent genuine slam contender) the story is completely different. It would then not make any sense to draw any conclusions from such losses other than it was one of those losses that just happen from time to time; like Sampras losing to Yzaga/Kucera (or Federer).
