Nintendo lifts European eShop age restriction
"Following analysis of the Parental Controls system on Wii U and Nintendo 3DS in cooperation with USK, the German Entertainment Software Self-Regulation Body, it was deemed that Nintendo's Parental Control system was found to have proved itself in practice," Nintendo informed European fans, as reproduced by reporter Daan Koopman.
The "in practice" bit answers our question of why the USK didn't make this decision until the Wii U had been available for months, and the 3DS for two years.