It makes a lot of sense to put these 6'6" guys on the D line. As long as they can be successfully coached to get down and play low (and they are), you've got yourself big, athletic linemen who can use good technique to get their leverage, but who can also get up and obscure the QB's view, tip passes, give chase and make tackles in the open field, and eat up blockers/slow down runners with their wingspan. And as long as they're being taught good technique, that extra wingspan will help them fight off offensive linemen as well.
We just saw how a successful a tall D line can be when they're well coached this season. It was almost like having four DT/DE hybrids on the line who could each do it all.