Certain personnel qualified for the OSM Afghanistan by supporting the initial operations there from out of theatre locations. Their medal did not have the clasp 'AFGHANISTAN' though. Ergo, they would not be able to wear the rosette on the ribbon bar.
A combat Infantryman in a Patrol Base gets the same medal as a clerk in the air conditioned comfort of Bastion, Lash or Kandahar. It's just a campaign medal, not a combat clasp.