I have taught similar types of classes. However, actually performing heavy work while wearing full PPE is something entirely different, which I have also done. I've always taught students that eight hours in a negative-pressure respirator is the equivalent of at least twelve without, when it comes to wear and tear on the user.
I really don't think someone could work effectively for 80 to 100 hours a week for weeks on end wearing such equipment. They might be able to put the hours in, but they wouldn't accomplish much. IMHO.
A friend of mine works for a nationally known insurance carrier who sponsored him and others to oversee health and safety at Ground Zero.
Compliance really wasn't even considered...they just did the best they could to to help the rescuers not do something stupid and kill themselves or others.
Respirators were available but not widely used for the reasons you described.
I made a visit to The Hole about October 2002 and it was still the saddest place I've ever been.