I saw a level 50-something Juggernaut (or maybe a Marauder - can't quite remember, but definitely a Sith Warrior) on the Imperial Fleet the other day. I thought his outfit looked cool so I inspected him to see what the pieces were. To my amazement he was kitted from head to toe in Willpower gear.
So I guess it's more common than you imagine.
I'm not saying this is the case, but with something like that it's possibly the result of some bad advice. I was once in a WZ where, while waiting at the start, a Sentinel asked, "Sorry to be a noob but I've seen some medium armor with Cunning and some with Strength. Which am I supposed to use?" I answered strength... everyone else answered cunning.
Now, you'd think a Jugg would get the hint by 50 after seeing all his armor selections from rewards are not only heavy armor but strength-based... but you never know. Or maybe he was roleplaying?