Just had a chat with support about your ticket on this issue, and it appears it's due to the fact that the things you want to block are not in the URL but in a querystring associated with the URL.
in a URL like http://some.server.com/some_resource.ht ... uerystring
the query string is not actually deemed by the HTTP spec to be part of the URL, and it's not actually passed into the PureSight plugin, so it can't filter it.
You can filter it in WinGate policy though.
Various search engines may search by different methods, and this even can change over time. Currently most use the GET method and pass search parameters in the query string (e.g. Google, MSN and Yahoo), but it used to be popular to use the POST method and submit it as a form, in which case the search parameters are in the message body sent by the client.
Filtering searches in WinGate 7 is very simple with policy, but in WinGate 6 it's more difficult with the current framework. It's a reasonable idea, but we haven't had requests before for filtering searches by any other means.