Nintendo is blocking Wii U content in Europe which is rated 18+, regardless of how users have set up the console's parental controls.
According to a post on NeoGAF, and confirmed by Eurogamer, any 18-rated games available on the system for purchase are only able to be viewed or downloaded from 11pm - 3am.
When the GAF user contacted Nintendo Italy customer service on the matter, he was met with the following reply:
"Dear customer, we would like to let you know that Nintendo has always aimed to offer gameplay experiences suited to all age groups, observing carefully all the relevant regulations regarding content access that are present in the various European countries.
"We have thus decided to restrict the access to content which is unsuitable to minors (PEGI) to the 11pm - 3am time window."
Eurogamer tested the claim, and found it was unable to digitally purchase or view information pertaining to Assassin's Creed 3 or ZombiU.
"You cannot view this content," a message read. "The times during which this content can be viewed have been restricted."
Of course, the same cannot be said for Xbox 360 or PS3, as users can view any and all content at any time of the day unless parental settings are in place.
We don't own a Wii U, so we are unable to test if this is also the case in North America, so we'll send a mail and ask.
In the US, content is governed by the FCC, which prohibits airing "indecent" material over the air between 6am- 10pm. Premium cable channels, such as HBO, Showtime, etc., are exempt.