I managed to construe nothing. Duff was playing left midfield for his club Blackburn at the time whilst Kilbane was playing left midfield for Ireland. How you can say McAteer, a right side midfielder, was played instead of him demands a manipulation of the facts that I can't quite seem to get my head around.
Could McCarthy have dropped McAteer and played Duff right midfield? Of course but it wasn't a position Duff had been playing for his club regularly. However the obvious place to play him would have been at the position he was used to playing, left midfield, in place of a player who IMO was considerably more limited than McAteer.
While as stated it may be true that after Mick left Kerr played Kilbane and Duff together, you are economical with the whole truth. This was mainly due to the fact that McAteer at that time was 33 and his International career was at an end. Also at this time Duff had been used mainly as a right midfielder at Chelsea once Robben arrived and had proven to be comfortable in that position, something he hadn't been expected to do at Blackburn. Also implying that because Kerr selected both that in some way exonerates McCarthy is flawed in the respect that Kerr was proven to be lacking tactically on many occasions during his tenure as manager.