I don't see how making this a public issue is a win for Google. Seems like something they should have kept in their back pocket. "Keep your enemies closer", as they say.
Whether or not people perceive the claim as accurate or complaining or whatever, first impressions are still powerful. If the first time you hear of Bing is the accusation that they're copying someone else's results (true or not), that's probably not a first impression you would want people to be left with if you were Microsoft. Chances are, people are going to read this as "My trusted search provider accuses unknown search provider created by the same people as Windows Vista of stealing its results".
Google can and does track clicks from Bing via Google Analytics. Every time you click a result on Bing and land on a page using Google Analytics, Google knows about it, and they record your Bing search terms from the referrer. The same is probably true for pages with Google ads.