I am slightly confused with people saying that "we don't need shields because we have Young & Willis, and Brads injured a lot anyway"
I would have thought that since Brad has been at Wasps, both Willis & Young will have hardly played, due to injury!. I get that Willis & Young are a great pairing, but their injury record is pretty dire and I would expect Dai to be looking to keep as many top quality players as possible. Its no use having only 2 great flankers, wasps need at least 4, better still, 6 top quality back row to compete over the season.
I might also suggest that Brad may not be on the stratospheric wages we may think. Bear in mind he came to the Prem so he could play for England, thats been his target, so he may have accepted a lower offer because it was in his interests to do so. (i'm not suggesting he's on a low wage, but I don't think he'd be up there with Hughes & Piatau at Bristol, for example)