What was vague about the responses? Google issued something like three separate denials the day the news broke, with increasingly clear and strong language. They stated they had never heard of "PRISM", at least not by that name, and that there was no direct access or backdoors to their servers. They also acknowledged, I believe, that they get FISA requests for user data but that they weren't allowed to publish statistics about them. I honestly can't think of much else they could have said, short of releasing the exact numbers they're not allowed to, to clarify the situation.
Googles response do not answer any of the following questions:
Do Google allow NSA to run computer code on google's servers? More specific, do NSA supply database queries when demanding data? Do NSA ever provide Google with tracking code like JS or links to NSA webbugs (1px imgs) that Google later put in targeted ads? Do Google ever provide physical (or remote) access to servers, hard drives (like backups) or network devices to NSA?
Having NSA supplied querries running over all of googles databases are indirect full access to googles servers. That as bad as direct access/backdoor, and would likely be called as such by NSA. Same goes for trackers inside google's adnetwork, or if they got physical access to any backups.
