I remember chats about different materials (in addition to sizing issues) coming up a lot when these first came out. I have three, and the first one I got is very soft, but the other two are more standard T-shirt fare - they'll probably feel fine after they've been washed and worn several times (which likely won't happen due to those same sizing issues), but at the moment they're slightly itchy and will never be nearly as soft as the other one.
I couldn't tell you the reasoning of this, though I hope they give the softer material another go. It really does feel nice.