Last time this came up I realized that Google is denies overspecificly everything that is not wiretapping. So my take is, that Google is saying "no direct access to the Google servers," as in no access to the actual boxes, while NSA and Guardian use servers in a somewhat looser sense. So my speculation is, that the NSA sits between the TLS reverse proxy and the actual servers.

( The mentionend post for reference and sources: https://news.ycombinator.com/item?id=5965994 )