The assumption isn't bad - it's a private network line, not a public internet connection. Nobody else had access to that line, at least they weren't supposed to. Splicing a fiber line is a bit outside the scope of your random attacker. You can't blame Google for not anticipating a hostile break-in by the government. The discussion should absolutely, 100% be directed at the NSA here. To accept that a private network connection is open season for the government to tap is batshit insane.
> Moreover, it is not clear if other governments or criminals also had access to the users' data (e.g. in Google's data centers located outside of the US). So far Google did not produce any public post-mortem thus we have no clue how bad was the problem.
How is Google supposed to tell you if they themselves didn't know?
Although from the leaks it sounds like everyone is fucked thanks to the GCHQ and the NSA getting friendly with each other.