That graph comes courtesy of Mike Fast, who published it as part of this Baseball Prospectus article. You’ll need a subscription to read the whole thing, but the gist of the article is that Rafael Soriano and Mariano Rivera aren’t so different. Both guys throw cutters as their primary weapon, which you can see in the graph, but the most interesting part was that Soriano started throwing the pitch more to left-handed batters in 2010 than he had in the past. The result was a few more popups and the best performance against lefties (.267 wOBA against in 2010, .313 wOBA pre-2010) of his career. Before 2010, Soriano went after southpaws with a little two-seamer away that resulted in ground balls and ultimately more hits.
Soriano will undoubtedly see his performance regress a little bit in 2011 because a 16.7% infield fly ball rate and a .212 BABIP is unsustainable, but there’s tangible evidence that suggests his improvement against lefties is real. He altered his approach against them, and the early returns look good.