I have always been curious to this question. Will different grip size lead to different Balance point? If not, how do they control the weight distribute? By adjusting the handle or increase/decrease shaft/frame material?
Yonex is more advanced. They vary the depth of the hole so that the racket meets the spec without needing additional glue or weight.
Some good answers here already. I have changed the handle on a couple of rackets, and both wood type and glueing affects the racket properties in many ways. I am quite sure the manufacturer makes an effort in the design of the complete racket to keep it within a certain specification range, but they can probably use a number of techniques to control the weight and balance point of the racket.