Why would they ever take Williamson at 7 if he would/could be available at 18? That's a move the Bengals would do.
Because I think the whole concept of 'maximizing your value' in the draft is so overblown. Media-moguls and couch potatoes have overblown this concept. There must have been a handful of teams who were high on Kevin Williams and deemed him 'over-valued' to be drafted in the top-10. I am sure those teams would trade their 'value pick' for Kevin Williams now.It is important to draft the best player available, regardless if you think you can get him later; there are no guarantees.
This is an unspoken rule in the NFL and more teams fall victim to it than is actually publicized. I have never once heard a team say, "We really wanted player X, but thought we could trade down and still get him. Team Y suprised us and took our player that we thought would slip, so even though nobody out there can see it, we really have a lot of egg on our face."