my understanding is that it is more salary based than pure skills.
The trouble is that the capping salary can be different from one player to another (and from one position to another). Although depending who you talk to, some people say that this is because there are sub-levels on potential.
I prefer the view that there is one formula for skills capping (unlike salary where there are 5 formulas). And although it correlates well to salary, it is not a perfect match.
Run of the Mill Canadian Manager