For the two handed tequnique Joe needs low and even action. Meaning the string height cannot change much over the length of the fingerboard. (see action set-up)
If there is too much change in height over the length of the fingerboard it would be like playing a piano with random key sensitivity and size. He wants to be able to push down any string anywhere on the neck with equal pressure to sound the note.
What Joe has pointed out is that when the guitar is set up correctly for his style the strings compress as oppose to buzz the harder there hit. He also found that this compression happens best for him with the .09 to .042 gauge strings. For the record he uses D'Addario.