Balance is a continual work in progress. The designers do an incredible amount of testing to ensure that the changes that get made are good ones and each change goes through many, many iterations before reaching it's final form. Obviously, whenever something does change, it directly effects something else. Hence, balance patches need to be spaced out to ensure the proper amount of testing.
That said, currently the heroes that need attention are getting it. Since we just put out a balance patch, we need to see how the changes work out before knowing exactly how the balance is currently shaking out. Plus, we are already looking ahead to what the next balance patch will contain.