We asked Google directly, and it tells us that on this occasion, the additional text is merely a clarification of the existing policy. It's spelling out what it already does. We spoke to London-based media lawyer John Haggis about this kind of amendment, who confirmed that if there were significant changes to the meaning of the policy, then Google (and others, like PayPal's shown below) would have an obligation to communicate that to its users. Not doing so would be an incredibly risky strategy for any firm. Minor housekeeping and clarifications, however, might not warrant a (potentially alarming) email blast -- though this recent Google case shows that it's still worth considering your strategy every time.
For those that were concerned about the specific part in Google's TOS that refers to email you receive (i.e., that sent by people who might not have agreed to said TOS), Haggis reminds us to think along the lines of how images, etc. are shared on Facebook. You might not be on Mark Zuckerberg's social network, but a photo you took and sent to a friend could be. Facebook might even learn it's a picture of you via tagging, and have a moderate profile of you based on multiple such photos. But, the truth is, there's not a lot it can do with that information if you're not a signed-up (and contractually agreed) member.
The more important issue highlighted by Google's recent tweak is of what little choice we have either way. It serves as another reminder that some of our most precious data is locked into services and ecosystems that we can do little to control or negotiate with. If your email provider incrementally changes its terms of service, you might not even really know what you've agreed to anymore. Worse, you could actually know all too well, and decide that you no longer are comfortable with those conditions. But what are your options, then, if a service goes a bullet-point too far? For the most part, you're left with the binary choice of suck it up, or find another provider. Here lies the biggest problem facing you or me. Who wants to change their email address after double figure years of distribution? Or migrate their music collection from one corner of the cloud to another (not to mention whether you can take it with you thanks to rights restrictions). Not many we'd wager.
The good news? Google tells us that for future such amendments it will be placing an "Updated" notice on the Google.com homepage (including on mobile), which will also show on regional domains (Google.co.uk, for example) when applicable. This might not solve your data-hostage quandary, but it should mean fewer false alerts.