My thing is that I don't think the WR's are significantly better than OG's like Green/Zion, or possible defensive prospects like Karlaftis/Dean/Lloyd, which is why I'd go elsewhere.
Generally I agree that if the WR were the clear BPA you do it, I just don't see a scenario like that happening here, even if someone like Wilson or London were available.
And it's not just Pierce/Shakir, those are just my favorites, but I'd be fine with Calvin Austin, David Bell, Metchie, Jalen Tolbert or Wan'Dale Robinson in the 3rd also.