My guess is it's a database thing: Deleting one post requires only 1 PM. Deleting one topic can require thousands of PMs.
...Yet TryNinja's bot handles that nicely.
My take is that it doesn't work.. because it's not implemented.
I don't expect it to be hard to implement as one mail per post, but then it may cause bitcointalk mails be seen as spam by various mail services.
And if it's done as one mail with all the relevant posts in it, then the mail may become big.
OP already created a new topic, which hasn't been deleted yet.
I know.
...and I guess that only the mod who has removed the topic can tell why he has done that.