I agree with smooth's assessment about stake vs. SP. I could have been clearer about that in my post. The way it is right now, it's possible to power down and sell Steem without necessarily losing any Steem Power from week to week - IF you are actively receiving rewards from posting and curating, and even from being a witness. And I suppose there's nothing inherently wrong with that since work is being done, but it can contribute to a seemingly endless cycle of powering down and selling from the same large SP holders.

The 13-week power down schedule effectively eliminates that possibility.