Let's say that Shanahan decides he won't be able to get a quarterback he's in love with at the four pick.
The Ravens excellent (and still very young) left tackle has only been given a first round tender, not first and third. If the Redskins draft Russel Okung they will be hoping that he develops to Gaither's level. There is a much larger probability he will be adequate but not Gaitherish, and a smaller but not insignificant possibility he will just be lousy.
Why not overpay Gaither a little and hope the Ravens choose not to match? Yes he has had some injuries and therefore poses a risk. But isn't he still less of a risk than a rookie?
The Ravens already have Michael Oher on hand... so they just might be willing to let Gaither go.