Yeah, I think there can be some variances in grip or the angle of the hand/wrist at release that can cause some guys to throw a "sinker" and some to throw a "2-seam fastball". Traditional "sinker" guys usually rotate their wrist some so the palm of their hand turns out somewhat. Maybe some "2-seam" guys control it more with finger pressure and the depth that they grip the ball. But they are very, very similar.
Some guys, like Corey Kluber have a 2 seamer with more horizontal movement, those guys work all over the strike zone with it. Some guys have more vertical movement, seems like those guys usually work down in the zone with it primarily (Trevor Cahill comes to mind initially, just since he was on the Cubs last year and I'm a Cubs fan). Then there are freaks of nature like Greg Maddux that could make the same pitch move in a variety of ways whenever he wanted, and still maintain perfect control.
Somebody with more pitching experience would certainly be able to describe it better than I just did I'm sure....
