So they are guilty for providing secure online storage. Apparently you aren't allowed to supply secure storage, you have to snoop through your users content to make sure its not illegal... Also land lords much search all apartments, banks must search safety deposit boxes, storage rental owners must search their units.
If they provided secure online storage, they shouldn't be guilty. If they were providing secure online storage to people whom they knew or should have known were hosting porn of underage people, they should suffer a significant legal penalty. If they were providing secure online storage to people whom they knew or should have known were hosting child porn of preteens then they should be burned at the stake.
There is such a thing as willful blindness. The sheer quantity of data involved is going to make it really tempting for someone to infer knowledge, but network management practices may or may not show it. Maybe the hosting company was just told it was a porn site, but it is entirely possible that they knew. In a good system a responsible prosecutor or cop should try to figure out whether they knew, and then a jury will decide the outcome.
(Plea bargaining is the problem with this scenario--there's a factual determination which should really determine the outcome of the case, but at least in the US the plea bargain system would make going to trial a very, very risky process for the innocent.)
Interestingly, this may be one of those few examples of a case where Snowden-esque monitoring did some good. Didn't news that Canada was trying to monitor all transmitted video on the web hit the news a little while ago? The timing of this suggests that this could stem from that.