Stevie can defend just a little bit. You are better off having midfielders that can fulfill the role of both attacker and defender. Stevie can do both.
I don't know where this 'defensive midfielder' idea has come in. It seems a very European thing. Anyone who thinks Viera or Keane are purely 'holding' midfielders is wrong. I saw Viera charging down the field ahead of all the attackers at the weekend and Keane gets forward a damn site more that Hamman.