Thanks for your post.
Unfortunately, this is not very visible at 'All Servers' level. The idea was that if you change something at this level then it becomes default for you. Though you can see how many have changed (from factory default) by seeing the number against 'All Servers' level.
It would be nice to know why you would like to know what has been changed from factory defaults at 'All Servers' level?
Note: You can always retrieve this directly from SQL Monitor database repository.