Well, It has something to do with mechanics. But in a certain way. Pitchers throw what works for them. Tim wakefield, for instance, throws a knuckle and a fastball, but that's because the knuckle works for him and the fastball is there to keep them out of balance. I, for instance, I can't throw a good change, so I will stick with what works for me, a curveball, a fastball and a slider. Now we come to mechanices, if you throw sidearm, you will get a hard time throwing splits, so you might as well throw a sinker, while it works better as a sidearm pitcher. But it just has to do with what works for you. I guess you are right with the Dan Haren-split-finger thing, but I'm more like a Santana guy, does that make me a circle-change pitcher? Probably not, I can't throw change so well, but I'm working on it:P.