If you read between the lines of that old thread, it would appear that something in the forum software/configuration is not quite up to spec. It seems from my experience:
EITHER we can have no e-mails from posts in threads (as it is now)
OR we can have an e-mail every time there is a post in a subscribed thread, even if the user profile says no e-mails - which can be MUCH TOO MUCH!

Perhaps Linda can tell you more . . . .