What have they done to earn your trust so that you believe them?
In matters of espionage and mass surveillance, I expect lying to be the default response for the government and corporate players involved.
They're saying PRISM gets them access to Google/Facebook/etc.'s data with no other middleman. That's not always the case; when working with international partners NSA might obtain intel from other (foreign) intelligence agencies, or their HUMINT might report data that is itself hearsay.
So the source/provenance of data is very important for an intelligence agency. NSA is saying this (with PRISM) is the best case as far as the source of intel goes, there is no better primary source.
That still doesn't mean NSA has embedded backdoors or that the company doesn't control access to the data though. Data Access is a separate concept from Data Source in intel.
We can still say that having this kind of access to data is above the capabilities NSA needs to have (it certainly seems ripe for abuse) but it's sounding like the reality is not quite as sinister as Greenwald or WaPo had been led to believe.
Inferring he is no longer CEO and might not know about these matters is just an informal fallacy and has zero to do with whether or not Google, Facebook, etc. is telling the truth on the matter. FWIW, I believe them when they say they aren't giving direct access to their servers to the government. That doesn't mean they aren't, and I'm willing to listen to any substantial claims that they are.
I don't trust the government to always do the right thing when poking around in our business, but I'm also not going to run around like a chicken with my head cut off when everyone gets their underwear in a knot over leaks like these.