I was reading a post and someone joked "Well i can do scales in G and C!!" And it kind implied people specialise in certain keys, get really good at them in particular! I thought this because Slash plays most of his solos on an album in the E pentatonic!! So maybe its like the first he learnt and he's way better at it. Dya think some people learn for example E pentatonic, an A major, a C minor, so they dont have to worry about moving the scale up and down and stuff. Because i find it easy to learn a scale but then sit and work out for ages how to transpose it and where the roots are and stuff!!