He wasn't before the latter part of his career but at that time he would almost always have a holding midfielder like Nicky Butt or Kinsella in beside him. An interesting stat that shows the change in Keane's roles at club level is that it took him over 50 games to score his 50th goal for Man Utd.
I agree that neither Barton or Ireland are holders but chances were Barton played that role when they both played in the centre. Barton scored 6 goals last season and Reyna was his partner for 5 of those with Ireland starting none of the 6.
I just think every manager gives 1 player the holding role in every match these days.