We've had this discussion before. You can throw in the "perfect gg gear" in D3Planner and you'll see that in the long run, dex/str is better. You get enough all res from diamonds and all res on gear, but if you switch all your gear to int then you lack a ton of armor.
Without seeing the barb's profile, my guess is that he has a wizard for key farming (honestly - who hasn't, wizards are just sooooooo freaking fast) and found superb support items on his wizard... therefore int rolls. Having a few pieces here or there also doesn't matter. But in general, you want dex/str on support classes.
As I've said, it has been discussed before on here, including the math; I think in season 7 or so, but I don't know in which subforum so I don't even know where to start searching for it.