I agree. I haven't "tested" anything firsthand, but I have been doing a lot of observing. It definately does seem that leather sales are very profitable. Especially the light leather durring the early stages (like what we are in now). I see that cloths sell at good prices too, as they are a loot only type of item that is also required in bulk. Mining materials seem to seel pretty well, but at slightly lower prices than leather and cloth at the moment. I think that once people start leveling up, mining will have higher profits, but it will come at a slightly higher "risk."
As Scudd said, leather is easier to fight for because, well, you don't have to. Veins on the other hand are "get it before the other guy does" types of things. I didn't know that you needed leather working to turn pelts into leather. That adds a new dynamic. That means to sell leather, you must spend both profession "point" on it. Due to that, and the fact that I want to stick it out with enchanting, I think I am going to choose mining instead. I think the big potential for mining will come at later stages of the game, once the crafters are leveled up and they really need that hard to find gold ore, etc. The market is also slightly bigger, because you have blacksmiths and engineers demanding it.