Did I miss some information? I only saw two slides. One that show the potential data accessible and one that show when the companies were added. It doesn't say exactly that they had access to everything.
As far as we know PRISM can simply be there to centralize the information that the NSA got in legals ways. We do know that the government ask about 100 users account information each day to Google, we can guess that they do the same to every company on that list and they were all added to PRISM at the date you can find on the slides.
I mean that slide contains one of the most important information that we currently have to guess the magnitude of PRISM, the budget. They only need 20 millions $ every years. True data mining is much more expensive than that.
If that is true, why would we expect that Google officials would be able to make any public confirmation of the Top Secret program? And, given that, why, in that case, would we expect the truth to be "in the middle"?
Conversely, if the leaked document is not genuine, then I still don't see any basis for expecting the truth to be in the "middle" between the false document and the Google denial.