Just seems to me that mostly-secret media interference is a less complex problem to solve than the type of pervasive surveillance that requires installing extra rooms of equipment at numerous telecommunications nodes around the world. And we have confirmation that the latter has happened, at least.
Granted, you would expect to hear rumors eventually, as lots of people would have to be involved and still manage to both keep their mouths shut and hide the activity from everyone else.
A set of random tosses of a coin (even if the coin is partially biased) is expected to produce a mix of heads and tails outcomes. The random toss here could be human error or undiscovered bugs.
On the other hand, the international order is relatively old. There is no ageism in geopolitics, just ask Henry Kissinger. Established social and political affinities exist, globally. No assumption whatsoever is made regarding an existing, international, and powerful network of individuals and organizations.
Given that such networks exist, and that the stakeholders are indeed powerful individuals and organizations, and further that this case is shining a spotlight on their manipulating social institutions under their control, in a case where an individual is being prosecuted for publishing material detrimental to these powerful interests, no assumption is required to consider the high probability of their use of their power (which is the entire purpose of gaining power, btw) to insure their position, their actions, and their criminal behavior, is kept hidden from the majority.
Occam's Razor.
We haven't had anything like a Marshall Plan or a Berlin Airlift for some time now.
If there was no such evidence, then concluding conspiracy based on what is happening with FB and Twitter would indeed be crazy.
Who wants to bet there is some extrajudicial (ah, sorry, "secret court") system to force prominent online actors to perform acts of covert censorship, in the name of national security or whatever? This would be an easy logical step from PRISM.