I read an interesting article today that convinced me that style is irrelevant, a true artists voice is determined by natural means and should never be forced. It seems counter-intuitive seeing how so many "famous" illustrators have such distinctive styles and adhere strictly to them. The agencies that hire these people also are more concerned with how well an artist's work fits their art direction they're already set on, and the more distinct it is, the better.
The illustration for pay world aside, I do believe a solid foundation in theory is absolutely necessary. This brings me back to Chuck Jones and his mixing of hard edged forms with sweeping arches. His lines of motion plainly seen to develop the action of the pose with as few frames as possible. His characters have such a sense of weight and balance that we truly do feel like we're watching a world of toons.