dthe g. Your article by Harold Hillman 2010)seems to have very little in the way of sources or peer review. This makes the conclusions of one individual very suspect.

The New Scientist:"Neurophysiologist Harold Hillman has a serious career problem. He's out of step with his peers, and now he's out of a job as well."(1988)

The fact that most western legislation mandates pre-stunning prior to slaughter does rather lead to the assumption that this pre-stunning serves a useful purpose. i.e. it reduces suffering. I think it is fair to say that this legislation in each country was drafted with veterinary input and so far the case for stunning animals being more humane is overwhelming. Even most halal meat is pre-stunned prior to slaughter(around 80%, depending on sources) The only exemptions granted are on religious grounds
    A review of news items on abbatoirs would suggest that more needs to be done to police behaviour of slaughtermen to prevent cruelty to annimals while being processed. CCTV was supposed to be placed in all slaughterhouses. I donot believe this has yet happened.