ColourOfSpring - 9:24 am on Jun 5, 2013 (gmt 0)
I have no idea. Perhaps it's a kind of trust building exercise / "truth commission", where Google is "prepared" to restore a site back into a higher level of trust when it removes links and/or disavows them, if it first admits to it's bad practices.
Then in reality Google don't just devalue the links, they penalise the page that the links point to in some way, and that penalty can only be lifted through paying some kind of penance through disavowing the links. That can be the only explanation. If Penguin DOESN'T go further than merely devaluing the links, then just let Penguin accurately pick off the links it doesn't like - why do it yourself through the disavow tool?