Contador used to rock up and boss Castilla y León, which was 2.1. Evans won the 2.HC Critérium International as defending Tour champ, Tour of Oman sees guys like those and Froome putting down markers for the season. It's not common, but it's not super uncommon either. The other thing is that after such a disappointing 2013, Wiggins is kind of going into "don't forget about me!" mode, and laying down a marker for the Tour support slots. Most Tour champions are in the position where they can ride what they want, they don't have that pressure, because most Tour champions aren't on the same team as the current Tour favourite.
So yes, it isn't something we see every day, but Wiggins has more reason to do it than most Tour winners too.