There's a difference between being a weak link and not being a big shirt seller. James has been the weak link in preseason for them in my opinion.
That said, Madrid will sell Benzema the second they get hold of someone better. That's just how they operate. Look at Di Maria, or Alonso. If they get Falcao then Benzema will be on the market, either this summer or the next. I think that's what Wenger is hoping for here.