Can you speak more about which ones and how that happened? The main one that comes to my mind is the British monarchy (to the extent that they don't really have much power), and my general impression (not a historian) is that that's a bit of a fluke. Looking at the French and American Revolutions, they sort of realized that their necks might stay better attached if they gave some ground. I'm not sure the monarchy being a participant in it's own reform is really applicable.