Not sure if maybe Wikimedia/Site requests would be the appropiate place.
When an user account is blocked on a private wiki that has the 'wgBlockDisablesLogin' in the config, the blocked user should not continue to receive email notifications about pages changed on his watchlist. This is happening to me.
Blocked users on 'wgBlockDisablesLogin'-wikis won't be able to login and check the change made, and there's the posibility that private data may be leaked in the edit summary (data that the user is not suposed to access anymore).
Since blocking on those private wikis such as http://noc.wikimedia.org/conf/highlight.php?file=private.dblist (& I'm speaking for those that I know: CU and steward wikis) is not used as a way to prevent abuse, but as a tool to remove someone's access to the wiki, it makes sense IMHO to disable from blocked users the ability to continue to receive email notifications. I guess that that is the primary use of the tool in all of the other ones.