I think because they have no one to compare him to. I am not sure how much the Mileage thing is relevant, but much of his HS carries were not hard carries, one cut and gone, and they believe he had a superior Oline, and that Bama some how makes RB's look better than they really are. He should be a 1st round imo, you cannot argue that he not only broke the SEC rushing record, but did so with less carries. He has excellent acceleration, durability, vision, size, and is a threat to take it to the house at any time. He had most of his best games against the best competition in the SEC, and while I do see a drop off at the next level........when loose, he is a NFL linebacker heading your way with the speed of a sprinter.
Bottom line? Both he and Eddie are/were 1st round RB's. Henry will be a 1000 yard back this years in the NFL. I am not buying that he is is not agile enough, his other qualities more than compensate. That is my subjective opinion.