All search engines look for keywords in URLs. That's why domain names with keywords in them are more expensive. If you're going to mine clickstreams from the toolbar, it's not far-fetched to think you would mine the entire source URL, including the query string, for keywords. Then there would be no need to postulate special treatment for Google search URLs, since the keyword is in plain sight (google.com?q=xxxxxx).

If that is what's happening, then the moral/ethical argument against Microsoft would have to be that they should treat Google specially, by explicitly ignoring clicks on Google's result pages. That seems to me to open up quite a can of worms.