Having watched him for a year, I think he just has really good command on one plane. It's not literally "pinpoint" command - it's more of a planar command.
For example, if he wants to throw the ball inside, then it's on the inner black / inside WAY more often than not, even if he frequently misses up and down on that inner plane.
Or, if he wants to keep the ball down, then he almost always keeps the ball down, even if sometimes he will miss his spot along the perpendicular horizontal plane (missing over the middle or further off the zone than he wanted).
So he seems more or less sublime at throwing to a certain plane, but not necessarily awesome at throwing to a certain point.... which could probably be a lesson to every pitcher out there who is struggling with command/control, or struggling with how to succeed without plus stuff.
And of course, Buehrle supplements all of this with speed changes. Dude pitches in 4 dimensions: up and down, left and right, hard and soft, breaking and straight.