Can't look right now but was this 'bug' introduced at some point in time?
http://www.ted.com/talks/edward_snowden_here_s_how_we_take_b...
http://ojs.uwindsor.ca/ojs/leddy/index.php/informal_logic/ar...
http://lesswrong.com/lw/ih/absence_of_evidence_is_evidence_o...
I'd say a Baysian analysis is a way to evaluate the veracity of an argument from ignorance, not necessarily a replacement of that argument. An argument from ignorance is a strict subset of a baysian analysis in which there is no causal relationship between the missing evidence, and the conclusion. This is such a case. So we can conclude by using a baysian analysis that this is in fact an argument of ignorance.
Unless, of course, you have additional statistical samples that show a non zero relationship between not knowing about NSAs activity and the fact that they are engaged in that activity.