I think that what he meant by that is not slow=easy, fast=hard, but rather that the greats can take something simple and make it sound good. For example, a lot of the stuff Slash played back in GnR was simple note-wise, such as the solos to Don't Cry, Knocking on Heaven's Door, Civil War etc. Some of them are so easy that a guitarist that has been playing just a few months could play, but most guitarists have trouble making it sound like him. His phrasing, accenting, dynamics are what makes it sound good.
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster
- Aqua Teen Hunger Force, The Universal Re-Monster