Cracked didn't read the entire article they cited ... firing percentages went up to 55% to 95% after changes in training. Stormtroopers displayed very good marksmanship in ANH. They boarded a hostile ship under fire, impressed even General Kenobi with their attack on the Sandcrawler, and in an incredible display of bravado actually faked a running battle with the rebels on the Death Star. These are not the actions of untrained conscripts who are afraid of taking (or giving) a life.
WRT the helmet, Luke's comment reflects the fact that the helmet's suspension wasn't adjusted for the size and shape of his head. He was significantly shorter than the average stormtrooper, and would have had a proportionately smaller head. He probably didn't know how to work the HUD, either. A trained stormtrooper would have no problem seeing in his helmet.