Hi Eric, the answer to the headline's question "Is Google Guilty Of Deliberate Query Sabotage?" is no. We've talked about the fact that results estimates are just estimates for years, see e.g. http://video.google.com/videoplay?docid=-4814548594071648913#
As to why the query [A B -C] can return more estimated results than [A B], that's easy to explain. The query [A B -C] causes us to go deeper through our posting lists looking for matches, which can lead to more accurate (and larger) results estimates. Other things can cause us to go deeper in finding matches, such as clicking deeper in search results.
Results estimates can also vary based on which data centers or indices your query hits, as well as what language you're searching in. It certainly has nothing to do with whether you're a "possible enemy of Google," as you put it.
We try to be very clear that our results estimates are just that--estimates. In theory we could spend cycles on
that aspect of our system, but in practice we have a lot of other things to work on, and more accurate results estimates is lower on the list than lots of other things.