Also Milos defeated Llodra and Verdasco (twice both), I think the problem is he's not well adapted to the surface yet. In my opinion It's true that a lefty has some advantage against right handed players, but don't believe it can be a decisive factor
I think it is the combo of lefty and the clay, which is really putting a ton of pressure on his 2nd serve. On hardcourts, his 2nd serve still gives him an advantage in the point, whereas on clay, he is getting more into 50/50 rallies. Add a lefty on clay, and instead of the return being a high backhand, it is a high forehand, and he isn't even starting the point 50/50. He has had numerous matches on clay where his (first serve %) x (% pts won on first serve) was higher than his (% pts won on 2nd serve).