The 1 extra mph lost on his pitches is probably a result of injury, and I don't think its anything to worry about long term (outside of age-related regression). I'm no expert by any means, but I do not doubt that the small range of his velocity in 2010 influenced his results. I'm wondering if he's tried to keep his velocity high to overcompensate for his loss of movement in his pitches.
One interesting blip on the chart was his wild uncontrollable game against the Yankees, where he hit Cano/Jeter-- his average velocity is considerably higher, but his control went way down. I also found it interesting that he seemed to struggle the most against better hitting teams-- the most glaring of which was the Yankees. 1/6th of his innings were against the Yankees, but he gave up 1/3 of his runs in them. Take those out, and he's at a 4.69 ERA. When 5 of your 23 games are against the best hitting team in baseball, and 3 of them in Yankee Stadium, it does very little for your average or confidence. For some reason, this gives me the impression that a good deal of his problems are in his head.