Don't you get it? Yes, you maintain control of him -- for one more year only. Then, he's out the door. Smart teams like the Patriots would trade him for a high pick (if they could get that) and draft another back to replace him. Turner is good, but he's not irreplaceable.
And as for your argument about controlling where he goes, that's silly -- the tender level decided that. Neither Denver nor anyone else is going to give a 1st and 3rd for him.
Superpunk is right -- A.J. Smith has mismanaged this almost as badly as he did the Brees situation. From this whole coaching fiasco and from what I've heard of him on ESPN radio, Smith is probably just hanging on for dear life. That's probably the real reason he is keeping Turner -- desperation.