According to the docs, you're supposed to get deletions in the stream, they should look like this:
{"delete":{"status":{"id":1234,"id_str":"1234","user_id":3,"user_id_str":"3"}}}
UPDATE: I did a few tests to see what was going on. First, I tried the filter URL with a track parameter, just like you are trying, and confirmed the same behavior that you are seeing. Then I tried a URL with a 'follow' setting instead, like so:
http://stream.twitter.com/1/statuses/filter.json\?follow\=1160471
When I try that, I get both tweets and their deletion messages. It's hard to know for certain obviously without asking Twitter, but I wonder if you just don't get deletions at all when using a track parameter, or if it's another issue along those lines.