They are different services. Facebook is a third-party platform in a way that GMail has never been. If your email address becomes your friends' Facebook data, your email address will be distributed to many companies that you have no direct relationship with. Who knows what those companies will choose to do with it; we choose not to find out.
GMail simply does not have this problem: there are essentially no "GMail apps", and users realize that their email addresses are exposed to their contacts when they use the service. There are no fly-by-night "GMail games" that will sell anything they can get their hands on to RapLeaf. This has its ups and downs, but one of its consequences is that "transitive trust" must have its limits.
Google is specifically demanding an API, and further making demands about performance, uptime, availability, etc. of the API. They're being perfectly clear that exporting the emails to .csv file that then gets uploaded is unacceptable.
And again, it's their service, and their servers, and I'm libertarian enough to say that they should be free to do what they want with them. However, I'm also free to question their "Love is Hate, War is Peace, Closed is Open" syllogism with respect to Facebook, and I find it preposterous.
GMail simply does not have this problem: there are essentially no "GMail apps", and users realize that their email addresses are exposed to their contacts when they use the service. There are no fly-by-night "GMail games" that will sell anything they can get their hands on to RapLeaf. This has its ups and downs, but one of its consequences is that "transitive trust" must have its limits.