Practical standards are really a drag.
Let's say every 3 months, to reflect all of the most modern changes in technical practise. After all, we all have such a good track record when predicting the future, don't we. In 1992 we were assured that Unicode was instantly going to be in mass use, for example. It takes years to adopt and deploy a standard. That means that we will never have any stability, since we will be spending all our time revising everything to be infinitely current.