Like anything you need practise, you don't become a sports star instantly it takes practise and training. I like to see it as when you start out with no experience [ie 0xp] you don't know anything about magic, when you do your first few skills you learn a few things, allowing you to do something more complicated. This works for practically all other stats. This also explains why theres such an exp gap between lvls, esp high lvls. It perhaps is because you've learned almost everything, and takes you a long time to finally learn a new technique, spell, item etc [ie a new level]