Occasionally these kind of things have happened that one driver in a team gets a lion's share of technical problems. Also if you flip a coin, there is a mathematical chance that you only get either heads or tails for a while.

Rosberg hasn't had a car-related DNF so far this year yet. Maybe it is bound to happen? Or maybe not. I remember back in 2010 I was expecting all season long for Webber to have technical problems (while Vettel had several of these), but this never happened... lol.