Microsoft just released data on its government requests (including FISA) too. For the last six months last year, Microsoft received between 6,000 and 7,000 government requests affecting between 31,000 and 32,000 accounts. [Microsoft]
The question remains, I think, to what extent the NSA has to "request" information via the PRISM program. Do these come through as discrete requests, or are they broad, blanket accesses? The slides seem to indicate that the PRISM program is a workaround, specifically designed to make it so the NSA doesn't have to make repeat requests (each time getting authorization from the FISA court). So I have doubts as to whether any information on discrete requests from these companies will reflect data handed over through PRISM.
This link offers a bit of analysis as to why the head honchos might be telling the truth when they deny knowledge of PRISM: http://www.usatoday.com/story/cybertru…
Basically, the article says that one way large companies may choose to handle these types of situations is by setting up very small teams, led by a member of legal counsel, to handle the logistics, and really be the only people who know about the program in question. That way, executives can enable, in this case, NSA surveillance, without being privy, themselves, to the actual details of what's going on. If this is how these companies are structuring their involvement with the NSA, would their official records reflect those data accesses? Or would the records still be isolated to those small, secretive teams? These are questions well worth asking, but I'm sure we won't get any straight answers even if we do.
In any case, it seems highly implausible that PRISM would even be necessary in the first place if the numbers of NSA data requests are as low as Microsoft claims. It's not that I doubt the accuracy of their figure based on literal requests, but rather that I don't think their figure is including the data handed over through the PRISM program (which may well not be accessed through literal requests).