NS records often change, especially in the additive, all the time. Google could do this all day every day and no one would notice. What you meant to say is that

NS records often change, especially in the additive, all the time. Google could do this all day every day and no one would notice. What you meant to say is that people would notice if MarkMonitor changed them without Google's permission. But that would never happen - they would certainly have Google corporate's permission before using this power. The geeks in engineering who care would hopefully object to a massive MITM surveillance system, but with their assistance is no longer required. And that's the beauty. Herding the cats in engineering at Google and Facebook to spy on everyone is difficult. Many of them might even quit their jobs before doing such a thing. Best to wedge a soulless anti-spam group between the happy consumer company and the Internet and get the blessing of a couple of CEOs who have been told that compliance is not optional.