In Obama-speak, "can't" means "we have a law that says they cannot, so they certainly must not be doing it."
In human-speak, "can't" means, "do they have a system capable of letting your average NSA analyst do this easily without oversight?" I suspect we'll never get the answer to this question unless it is leaked.
Let's at least take a wider view and recognize this is not Obama-speak, but is general political doublespeak. Obama is not the first to employ such language, nor will he be the last. Politicians, pundits, and the general media are working off the talking points we heard about earlier, and everyone is using the same words in the same way. As the executive, Obama is merely putting himself out there as another political actor joining in the shared deceptions, and all ought to be held accountable for this.
The buck stops with him, and honestly most people who support Obama expect at least a little better from him. This is why his approval rating is at an all time low this month of 47%.
In human-speak, "can't" means, "do they have a system capable of letting your average NSA analyst do this easily without oversight?" I suspect we'll never get the answer to this question unless it is leaked.