The titles belong to Warner Brothers, MGM and Universal, which are pulling them from Netflix and instead housing them in their own subscription-based "Instant Warner Archive" which you can access for $10 a month. (Oh, and according to the Instant Warner Archive's FAQ, content can be pulled from that library as well.)
While few people are likely to miss the 1,700 culled titles (which include such classics as Deep Impact but also a couple of classic James Bond flicks), Netflix is also ending its licensing deal with Viacom, which includes content from Nickelodeon, BET and MTV. Instead, Netflix said it would try to license shows individually from Viacom to get a better deal.
As content licensing fees increase, and content owners like Warner Brothers try to cut out the streaming middle man and go direct to consumers, Netflix has responded with its own original programming as well as more exclusive licensing deals to stand out from an increasingly crowded field. Still, the loss of these titles is another reminder that streaming subscription services are a fickle beast and living in a "post-ownership" society has its drawbacks.