I just had my USA BC Rich Mockingbird done
The operator inputs info like scale length, number of frets, number of strings. Then the machine goes and measures the fret high, radius on the frets and the fretboard, string spacing, exc... With the strings on and tuned to pitch. Then the strings are removed, and the machine re-measures everything. It does that so it can compensate for the removed neck relief. After all the measuring, the machine presents the data to the operator who then decides how much he wants the machine to remove from the frets. The machine then cuts the frets following the radius and locations it measured.
I work as a CNC programmer and operator, daily I'm working with +/- .001 inch's tolerances. The Plek machine's are VERY impressive IMO. After having my BCR Plek'd I measured the frets out of curiosity. My Brown & Sharp indicator said that all the frets are within just a little less than a 1/1000th (A hair on your head's about 3/1000th). I don't care who it is, a human IS NOT going to get the frets that level.
The reason that the Gibson's aren't as impressive, is that they are using templates, and not running the measuring program on the guitars. That will lead to imperfections, that compromise the fret work.