I noticed a few replies mentioned midichlorians, but what are midichlorians? The Jedi of Kreia's era believed the force was an energy field that was all around us, penetrating us. The ignorance of the Clone War era Jedi could have led them to believe that the force was only available via midichlorians(which would mean that the Exile would have had to cleanse herself of the critters.) In Ep IV Obi-Wan echoes Kreia's description of the force(or she echoes him) indicating that while in the Void Qui-Gon gained and passed on the knowledge of no 'chlorians.
But I digress, this is a debate for another topic.